Book - The Hormones in Human Reproduction (1942) 6
Embryology - 19 Apr 2024    Expand to Translate
|
|---|
| Google Translate - select your language from the list shown below (this will open a new external page) |
|
العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt These external translations are automated and may not be accurate. (More? About Translations) |
Corner GW. The Hormones in Human Reproduction. (1942) Princeton University Press.
| Historic Disclaimer - information about historic embryology pages |
|---|
 |
Chapter VI The Menstrual Cycle
SURELY the process of menstruation is one of the strangest things in all Nature. An important organ — the uterus — serving an indispensable function, is overtaken at regular intervals by a destructive change in the structure of its lining, part of which undergoes dissolution with hemorrhage, and must be reorganized in every monthly cycle. The loss of blood from organic tissues, everywhere else in the animal kingdom a sign of injury, even of danger, is in this one organ the evidence of healthy function. To make the puzzle greater, menstruation is by no means general in the animal kingdom, or even among the mammals. It occurs, indeed, only in the human race, in the anthropoid apes (having been observed in chimpanzees and in the gibbons), in the baboons, and in the Old World monkeys ; in short, in a closely related group of primates, one little portion only of the great class of Mammalia. No other animals, in forest, plain, or sea, hiding in dens or grazing the fields, undergo in the course of their cycles any such phase of hemorrhage. It is a paradox indeed that this curious phenomenon of periodic breakdown, seemingly an imperfection, a physiological flaw, is characteristic solely of the females of those very animals we are pleased to think the highest of earth's creatures (Appendix II, note 9).
The periodicity of menstruation. In human females, menstruation recurs at intervals of about 4 weeks. There is a common impression that the cycles are normally quite regular, but any woman who will keep an accurate calendar of her cycles will find a surprising variability.
A recent statistical analysis of thousands of records^ shows in fact that the commonest average cycle length (the "mode"
1 Leslie B. Arey, "The degree of normal menstrual irregularity." American Journal of Obstetrics and Gynecology, vol. 37, pp. 12-29, 1939.
( 135 }
THE HORMONES IN HUMAN REPRODUCTION
as statisticians say) in adult European and American women is 28 days, but it is also very common for a woman to average cycles of 25, 26, 27, 29, and 30 days. The individual woman, moreover, often varies several days, in any one cycle, from her own average. To state this in exact terms, so as to make clear just how much variation a woman may consider normal, is rather difficult, for it is a matter of statistics and such things are hard to translate into everyday language. The clearest statement is that of Professor Arey, already quoted, whose words I paraphrase as follows: let a woman keep a record of her cycles for several years, so that she has enough observations to strike an average. Say, for example, that her personal average is 28 days. Arey's figures show that with this information she cannot hope to predict the onset of any given period with accuracy closer than 2.5 days plus or minus, i.e. she may expect it any day between the 25th and 30th after onset of the last period, and even then one-third of all her cycles will depart still more widely from the average length, say another day or two, and sometimes more. The statement that she averages a 28-day cycle has the same kind of meaning as the average price of eggs during the year, which may be very different from the price at any one time, or a baseball player's average of home runs per game. All it means is that the length of her successive cycles will be within a few days, more or less, of 28 days, seldom however coming out at that precise length. In fact a woman whose cycles were perfectly regular to the day, during many months or years, would be a medical curiosity. No such case has ever been reported.
When we come to consider, a little later, the intricate interplay of hormones that goes to produce the cycles, we shall not be surprised that the timing is not perfectly regular. Nor will we be surprised to learn that in young girls, during the first few months or years of menstrual function, while the endocrine mechanisms are becoming adjusted, the cycle length
{ 136 }
THE MENSTRUAL CYCLE
is extremel}'^ variable. Arey compiled the records of 100 girls during about two years after the onset of menstruation, and calculated the average cycle length of each during this epoch of their lives. One-third of these girls actually never had a cycle that corresponded exactly to the day with their own personal averages ; in other words, every single cycle varied from the arithmetical norm. During the latter part of adolescence there is considerably greater regularity.
The first menstruation most commonly takes place sometime between the ages of 12 and 14 inclusive. The average age at the time of onset, in the white race at least, is 13% years, but onset at any age from 11 to 16 may be regarded as normal. Delay beyond 16 is a matter for medical investigation.
The normal duration of the menstrual flow may be from one day to one week ; the modal duration is 5 days.
Among the infrahuman primates there is only one, the Rhesus monkey, which has been studied in numbers large enough for positive statement. In this species, observed in captivity in the United States and England, the mode, i.e. the most frequent cycle length, is 28 days, as in women. Individual animals have average cycle lengths of 25 to 31 days, and single cycles vary from 14 days up. Rather scanty observations on chimpanzees, baboons, and a few species of monkeys mostly show averages a little longer than 28 days. This statement might or might not hold good if the statistics were more extensive (Appendix II, note 10).
The poetic suggestion quoted at the head of Chapter III, that the reproductive cycles of living things are part of the rhythms of the universe, must not be taken too literally. Menstruation is not regulated by the moon. It happens that the lunar cycle has the same length to the day as the modal human cycle, but we have seen that the human cycle frequently deviates from the mode, and if, for example, the start of the period coincides with the new moon or any other given lunar phase, the odds are it wiU be off cycle by at least a day
{ 137 }
THE HORMONES IN HUMAN REPRODUCTION
or two next month and perhaps completely out of phase next season. I once had 4 females of the Java monkey (Macaca irus) in a cage adjacent to a large group of the closely related Rhesus monkeys. While the latter were running cycles of 28 days' modal length, their Javanese cousins, living under the same moon, were exhibiting a modal cycle length of 35 days. As mentioned in Chapter III, the cycles of other mammals may vary from 5 days to a year in length, and if we consider the birds and insects we finds cycles of one day to 17 years. If the heavenly bodies are to control these rhythms, the cycle of the 17-year locust calls for a hitherto unknown comet !
The idea of a relation between human menstruation and the moon is, however, ancient and widespread. It was, no doubt, suggested by the obvious and inescapable relation between the moon and the tides of the sea. If the moon can control the ebb and flow of great waters, why not also the tides of human life . Perhaps the popular mind has also been influenced by the fact that outbursts of insanity in women sometimes accompany the menstrual cycle ; this seems again to link menstruation with the moon, which has long been considered a cause of lunacy. Then there are, of course, certain special cases in nature in which the life of an animal is directly influenced by the moon or the tides (e.g. the palolo. Chapter III) . These cases may have helped to foster the notion we are discussing. As lately as 1898 the eminent Swedish physicist Svante Arrhenius thought he had proved the connection of lunar and menstrual cycles by mathematical evidence, but this has been completely disproved, notably by the English physicians Gunn, Jenkin, and Gunn (1937). It is indeed difficult to conceive of any direct participation of the moon in the reproductive cycles of the land-dwelling primates, for if it were really efl*ective we should expect menstruation to occur at the same phase of the moon in all females of a given species, a state of aff"airs that would have made the social organization of mankind unthinkably different from what it is.
{ 138 }
THE MENSTRUAL CYCLE
NATURE OF THE MENSTRUAL CYCLE
Events of the cycle in non-menstruating animals. To get a clear understanding of the process of menstruation, it is necessary to understand first what takes place during the cycle in animals which do not menstruate. This has already been discussed in part and illustrated in previous chapters, and is summarized in the diagram herewith (Fig. 19) which represents the typical or generalized cycle of mammals. If we wish to talk about any one species, we shall have to introduce modifications into this scheme, but as it stands it can be used as a basis for understanding them all. In the upper portion, which shows events in the ovary, we see (beginning at the left) the growth and ripening of the follicle. The moment of rupture of the follicle and discharge of the egg gives a convenient point of division, which we may consider as the start of a new cycle. Looking at the third part of the diagram, that indicating sex activity, we see that ovulation occurs during estrus, an arrangement which is adapted to secure fertilization of the egg. Next, the follicle is converted into a corpus luteum. This in turn runs its course, secreting progesterone for about two weeks (in typical species) and then, if the Ggg is not fertilized, the corpus luteum suddenly begins to degenerate and ceases to secrete its hormone. Thereafter, a new crop of follicles begins to develop. In some animals the new cycle follows at once (e.g. the guinea pig, which has a cycle of only 15 or 16 days) ; in others several months may elapse, during which the ovaries are relatively dormant (as in dogs and cats) or a whole year, as in many wild animals.
Digression about the cycle in general. We come now to the fundamental question of the female reproductive cycle, namely what causes the alternations of structure and function in the ovary. When the cycle was first discussed, in Chapter III, we could deal with it only as an observed phenomenon of natural history, but we are now in a position to consider
{ 139 }
THE HORMONES IN HUMAN KEPRODUCTION
{ UO }
THE MENSTRUAL CYCLE
the problem in the light of our knowledge of the hormones. To resume this subject where we left off on page 75, there is scarcely any doubt at present that the cycle is somehow produced by interplay of hormones from the ovary and the pituitary gland.
If we look at the pituitary gland or hypophysis (Plate XIX and Fig. 20) we find that this gland of internal secretion is composed of two major parts, the anterior and the posterior lobes. It is the anterior lobe which produces hormones (probably two in number) having the power of stimulating the ovary to produce estrogenic hormones and of promoting the growth of ovarian follicles. They also affect the male organism, causing the testes to grow and produce sperm cells. Because of these actions the hormones we are discussing are called gonadotrophic, a name which signifies "producing growth of the sex glands." From the brilliant work of P. E. Smith, Bennett Allen, H. M. Evans, Zondek and Aschheim, and many others between 1915 and the present time, we have learned (as mentioned in Chapter III) that removal of the anterior lobe of the pituitary stops growth of the ovaries and puts an end to the cycles of the animal. By implanting bits of anterior pituitary, or better by injecting extracts of the gland into immature animals, the ovaries are caused to grow and the cycle to begin. The ovary is thus absolutely dependent upon this action of the pituitary. Removal of the anterior lobe produces all the effects of castration, for without it the sex glands, ovary and testis, deteriorate to inactivity. On the other hand, there is a good deal of evidence that the estrogenic hormone of the ovary represses the production of the pituitary gonadotrophic hormones. After removal of the ovaries, the pituitary gland is found to contain more gonadotrophic potency than before; after injection of estrogenic hormones it contains less (Appendix II, note 11).
When these facts became known, a fairly clear explanation of the reproductive cycle suggested itself almost simultane { m }
THE HORMONES IN HUMAN REPRODUCTION
Post.
Fig. 20. Above, the pituitary gland, showing the anterior lobe and the posterior lobe with its stalk by which the gland is connected to the brain. Enlarged approximately 5 times. Below, median section showing position of pituitary gland in its bony cavity at the base of the skull; compare with the X-ray photograph, Plate XIX.
{ m }
w
^S, ^I^^^H
i]
^^^^^^|R^ â– â– â– iiiiiiilMr
^^
I^H
1
Plate XIX. X-ray photograph of the human skull, to show the location of the pituitary gland. The arrow points to the little hollow (sella turcica) in the bone below the brain, in which the gland lies. About 2/5 natural size. Courtesy of the Eastman Kodak Company, Rochester, N.Y.
T^vii
Plate XX. The human infant at birth, with the placenta and membranes. From the anatomical plates of Julius Casserius, published by Adrianus Spigelius in 1626.
THE MENSTRUAL CYCLE
ously, about 1931-1932, to a number of investigators, among them first perhaps Brouha and Simonnet in Paris, then to Leonard, Hisaw and Meyer in Wisconsin, and Moore and Price^ in Chicago. This hypothesis suggests that the cycle is Hke a clockwork in which the pituitary is the driving force and the regulatory escapement is the reciprocal action of ovarian and pituitary hormones (Fig. 21). The pituitary
ESTRUS
E5TRU5
HYPOPHYSIS
ESTRIN
Fig. 21. Diagram illustrating the alternation or "push-pull" hypothesis of the ovarian cycle discussed in the text.
makes the follicles grow, ripens the follicles and eggs, and causes the production of estrogenic hormone. The rising tide of estrogenic hormone thus checks the production of pituitary hormone, which begins to fall off as estrus occurs. The estrogenic hormone is used up, and as it reaches a low ebb, the pituitary, now freed from the repressive action of the ovary, again begins to secrete its gonadotrophic hormone. Up goes the pituitary and then up goes the ovary again, thus getting another cycle under way. This scheme, however, cannot fully explain the cycle. As Lamport has shown, a push-pull action of the two hormones would naturally tend, not to effective cyclic fluctuations of estrogen, but to ever smaller changes approaching equilibrium. We must therefore postulate some other event which occurs from time to time to break the bal 2 For a discussion of this theory, see Carl R. Moore and Dorothy Price, "Gonad hormone function." American Journal of Anatomy, vol. 60, pp. 13-72, 1932, and Harold Lamport, "Periodic changes in blood estrogen." Endocrinology, vol. 27, pp. 673-680, 1942.
{ 143 }
THE HORMONES IN HUMAN REPRODUCTION
ance of the two hormones. Under the push-pull hypothesis it is in fact easier to understand the long diestrous phase of cycles like those of animals that have an annual cycle, when (as we may suppose) the estrogenic and gonadotropic hormones are balancing each other, than to explain what happens to set the see-saw swinging again, or to bring on cycles, in some animals, every few days or weeks. At present we can only make vague conjectures about the possible role of other hormones, e.g., progesterone or another pituitary hormone.
Events of the cycle. To resume the main theme of our discourse, during all these changes in the ovary the uterus is, of course, constantly under the influence of the ovarian hormones. Even when there is a long anestrous interval between one ovulation and the next, the ovary produces enough estrogen to protect the uterus from atrophy. As the follicles enlarge and ripen, there is a period of growth and development of the lining of the uterus (endometrium). When the corpus luteum is formed and begins to produce progesterone, the uterine lining is rapidly brought into the progestational condition, as described in Chapter V and illustrated in Plate XVII. About one week is required to complete these changes. The favorable environment thus prepared for the embryos (pages 107-111) is maintained about one week longer, making two weeks in all between the beginning and the end of the active life of the corpus luteum. This is the progestational phase of the cycle. If the animal mated while in estrus, the embryos arrive in the uterus about the 4th day (later in some species) and begin to attach themselves sometime between the 7th and the 13th day, according to the species. It will be seen that the corpus luteum functions long enough to give time for implantation of the embryos. If this occurs, some sort of signal, probably via the pituitary gland, causes the corpus luteum to survive and maintain the uterus in a state favorable to early pregnancy.
Retrogression of the uterine changes. We are considering
{ lU }
THE MENSTRUAL CYCLE
here, however, a cycle in which the eggs are not fertilized. In such a case they are transported through the oviduct to the uterus, where about 8 or 9 days after they first left the ovary they go to pieces and disappear. The corpus luteum holds on until the 14th or 15th day, then degenerates and ceases to deliver progesterone to the blood stream. The endometrium is thus deprived of its hormonal support. The changes induced by progesterone disappear in the course of a few days. The blood flow through the uterus diminishes, the lining becomes thinner, the cells of its surface epithelium and glands diminish in number and height, and the glands resume the simpler form that characterizes the interval and follicular phase of the cycle. Generally speaking, the steps of this reversion are gradual ; it is spread over several days, and gives no outward sign to let us know it is in progress.
In our diagram (Fig. 19) the whole sequence of changes in the lining of the uterus is illustrated by the middle portion, which is a conventionalized representation of the glands in their successive phases.
The cycle in menstruating animals. The cycle of the menstruating animals and the human species is fundamentally similar to that of other animals. Two important difl*erences, however, exist. In the first place there is not a sharply defined phase of sexual receptivity like the estrus of other mammals. Although cyclic fluctuations of sex activity occur in some of the apes and monkeys, this is by no means as well defined as in most other animals, and in the human female sex desire is obviously much more influenced by all sorts of moods, social situations, domestic ups-and-downs, and the like, than by any tendency to cyclic alternation. Mating may occur on any day of the cycle. There is no outward sign, like the estrous behavior of lower mammals, to indicate the time of ripening of the ovarian follicle and its ^gg.
It is interesting to speculate about the effect of this suppression of estrous rhythm upon human life and the progress
{ us }
THE HORMONES IN HUMAN REPRODUCTION
of the race. Certainly our customs would be very different from what they are if the sexual compulsions of women were like those of animals with strongly marked estrous periods. In these creatures the sex response, intense and irresistible in the female during estrus, is wholly absent at other times ; in the human species it is moderated but diffused over a larger proportion of the time. In their various aspects and sublimations, from downright sex desire to affection and vague romantic yearnings, the impulses of sex color in some degree our entire adult lives, teach us to love nature and art, and call us to sacrifice and devotion. In this respect above all mankind differs from the beast.
Regardless, however, of this all-important difference of behavior, the cycle of the ovary proceeds in the human species as in the others (Fig. 22). The follicle ripens and ruptures, the egg passes to the uterus, the corpus luteum forms and takes up its endocrine function. The lining of the uterus undergoes a profound progestational change. The epithelial cells of its glands multiply so greatly that the glands have to become sinuous and pleated, in order to be accommodated in the available space. The glands fill up with fluid secretion and therefore become dilated. The result is a very characteristic appearance, when seen in sections of the uterus. This progestational or "premenstrual" state is well shown in Plate XXI, C.
Inspection of the diagram (Fig. 22) will show that the premenstrual phase is at its height during the second week after discharge of the egg from the ovary, just as in other mammals. If there is a mating, and the egg is fertilized and becomes an embryo, it will reach the uterus when the endometrium is fully under the influence of the corpus luteum and ready to take care of the new arrival.^ This is clearly illus 3 We do not actually know the time of arrival of the human embryo in the uterus, nor the precise time of its implantation, since no normal
{ U6 }
THE MENSTRUAL CYCLE
human embryos younger than about 7 1/2 days have as yet been seen. Information from other animals, together with what is known of the human embryo at the 8th day, makes it highly probable that the human embryo becomes attached about the 7th day after ovulation.
{ U7 }
THE HORMONES IN HUMAN REPRODUCTION
trated in Plate XII, C, a photograph of one of the earliest known human embryos, obtained by Dr. Arthur T. Hertig of Boston, and preserved in Baltimore at the Department of Embryology of the Carnegie Institution of Washington. The uterus in which this 11 -day embryo has attached itself is in the typical progestational phase, as shown by the form of the glands.
The menstrual breakdown. About the 14th or 15th day after ovulation, the corpus luteum begins to degenerate, as in other animals. The uterus, thus deprived of support by progesterone, undergoes a violent reaction. In its innermost layer the circulation of blood is disturbed, the surface epithelial cells, the glands and the connective tissue are damaged, and the tissues break down. Blood from small ruptured vessels fills the cavity of the uterus and trickles toward the vaginal canal. A section of the endometrium at this time shows a remarkable picture ; the surface layer has sloughed away, and the stumps of the glands jut into the central mass of blood and cellular debris. In the course of a few days a process of repair sets in, the lost surface cells are replaced, the glands restored and the debris cleared up.
The various stages of the uterine cycle are shown in Plates XXI and XXII, which present a series of specimens from the Rhesus monkey.
The sequence of these events is summarized in the diagram, Fig. 22. From this it will be seen that ovulation takes place about the middle of the interval between the two menstrual periods. It is customary to count the days of the primate
Plate XXI. Three stages of the cycle of the uterus of the Rhesus monkey.
A, 16th day of cycle, just after ovulation; interval stage. B, 23d day of cycle. Effect of corpus luteum hormone appears in the glands; early premenstrual stage. C, 27th day of cycle. Menstruation due one day later. Full progestational (premenstrual) stage. All magnified 10 times. A, Corner collection (no. 2)}
B, courtesy of C. G. Hartman (H. 326); C, courtesy of G. W. Bartelmea (B. 123).
{ U8 }
THE MENSTRUAL CYCLE
cycle from the first day of menstruation. Ovulation most commonly takes place about the 12th to the 16th day, although in individual cases it may be earlier or later than this. The corpus luteum is active for about 13 or 14 days, and therefore its degeneration brings on menstruation again 25 to 30 days after onset of the last period.
The "safe period.** Let us digress again for a moment, to discuss, in passing, an interesting and important deduction that follows from the schedule of the human cycle, as shown in the diagram, Fig. 22. There is evidence from many species of animals that the eggs can be fertilized only while in the oviduct, during the first two or three days after their discharge from the ovary. We know also that the sperm cells cannot survive more than a few days in the female reproductive tract. It follows that the only part of the human cycle during which fertilization of the egg can occur is the few days following ovulation. Since, however, there is no way of ascertaining the date of ovulation and it may vary by several days, we shall for the sake of caution estimate the presumably fertile period as a few days longer each way, say from the 8th to the 20th day of the cycle, counting from the first day of the menstrual period. All the rest of the cycle, i.e. from about the 20th day to the 8th of the next cycle, will be a period of sterility, during which mating will not result in pregnancy. This is the theoretical basis of the so-called "safe period" method of birth control. If all women had regular cycles and things never happened out of turn, it would no doubt be a fully effective method, but irregularity
Plate XXII. The uterus of the Rhesus monkey during menstruation. A^ first day of flow; at bl., small collections of blood in the lining of the uterus. B, third day; note loss of surface tissues of lining and disappearance of progestational pattern of glands. C, anovulatory menstruation, first day. Note, in comparison with A, that there is no progestational change of the glands. Magnified 10 times. Ay B, Corner collection (nos. 39, 22) ; C, courtesy of G. W. Bartelmez (B. 128).
{ U9 }
THE HORMONES IN HUMAN REPRODUCTION
of cycles and unpredictable variations make it much less than certain.*
Role of the blood vessels of the uterus in menstruation. Within the past few years a good deal has been learned about what actually happens to produce the menstrual breakdown. Much of this advance we owe to G. W. Bartelmez of the University of Chicago, and to his former associate, J. E. Markee, now of Duke University. To make it clear we must first understand the arterial blood circulation of the lining of the uterus. The endometrium is fed by arteries which come up into it from the underlying muscle (Fig. 23). These have branches of two kinds. Those of one kind are very pecuhar, for they are wound into coils, making their extremely tortuous way toward the surface, where they break
Fig. 23. Diagram of the arteries of the uterus, from the description of Daron. Enlarged about 20 times.
Carl G. Hartman, Time of Ovulation in Women. Baltimore, 1936. { 150 }
THE MENSTRUAL CYCLE
up into tiny capillary vessels (not shown in the diagram) that supply the inner one-third of the endometrium. The other kind of branching is that of the straight arteries, which run a short course directly to supply the basal two-thirds of the endometrium.
By studying under his microscope a series of uteri of women and monkeys, collected at successive stages of the cycle, Bartelmez showed that the fundamental step in the menstrual breakdown is a shut-off of the coiled arteries. With such material, however, it is possible to see only interrupted stages of the process ; the sequence cannot be seen in full. Markee has therefore made use of a remarkably clever means of watching menstruation in progress.^ Since we cannot see into the uterus, he undertook to put that organ (or rather, small pieces of its lining) into a situation where it can be watched. He grafted bits of endometrium into the anterior chamber of the same animal's eye, thus applying a method already used by a few investigators for other purposes. The small grafts are placed just behind the clear cornea, and get their blood supply through vessels which grow into them from the iris. The operation of grafting, which is done under complete anesthesia, is relatively simple, though, of course, it requires deft hands. The animal suffers no discomfort from the graft and is inconvenienced only by the fact that while under observation she has to sit in a tight wooden box, something like a pillory (but more comfortable), while the investigator studies her eye through a microscope. He is, by the way, at least as uncomfortable as the monkey, because the task of watching the winking, roving eye of the animal, changing the focus and moving the microscope and light whenever necessary, is enough to exhaust the patience even of a scientist.
5 J. E. Markee, "Menstruation in intraocular endometrial transplants in the Rhesus monkey." Carnegie Institution of Washington, Publication No. 518 {^Contributions to Embryology, vol. 28), pp. 219-308, 1940.
{ 151 }
THE HORMONES IN HUMAN REPRODUCTION
The grafts survive and grow. They respond to estrogenic hormone, injected under the skin, by swelling and growing just as if they were still part of the uterus. If the ovaries are removed, the grafts undergo castrate atrophy. Most astonishing of all, when menstruation occurs in the uterus, it occurs at the same time in the eye-graft, runs the same course, and ceases at the same time. The menstrual hemorrhage which occurs in the eye, stains and clouds the aqueous humor for a few days but soon clears away.
Markee was able to watch the process through the microscope, using low to moderate magnification, from 12 to 150 times. What he saw has helped us greatly to understand the nature of the menstrual breakdown, although (as we shall see) there is much still to be learned. Markee tells us that the first sign of impending menstruation in the eye-graft is blanching of the tissues due to shutting off of the blood flow by contraction of the coiled arteries. This does not happen in all the arteries of the graft at one time, but in individual arteries, so that blanched patches appear here and there in the graft, until all the tissues ultimately experience the blanching. After a few hours this phase wears off. Through the relaxed arteries the blood flows again with renewed force, but the tissues of the endometrium and especially the capillary blood vessels have sufi^ered from the lack of blood supply. Here and there the small vessels give way and burst, causing tiny spurts of blood into the tissues. The little pools of blood thus produced coalesce and drain into the anterior chamber of the eye. In the uterus itself, similar hemorrhages are of course discharged into the cavity of the uterus. After a few days this strange series of events is over, and the damage is promptly repaired.
With Markee's direct observations to guide us, the study of prepared specimens of the uterus is much clearer. Observations by the two methods agree perfectly, but without observations of the eye-grafts we should probably not have
{ 152 }
THE MENSTRUAL CYCLE
learned the importance of the periodic shutting off of the spiral arteries.
Coiled arteries of the type thus shown to be fundamentally involved in menstruation in the monkey are also present in the human uterus, but have never been found in non-menstruating animals. Menstruation, then, is primarily an affair of the coiled arteries, which control the blood supply of the inner layer of the endometrium and by their closure cause breakdown, tissue damage, and hemorrhage (Appendix II, note 12).
In view of the violent disruption that characterizes the retrogressive phase of the cycle in women and in the other menstruating primates, it is a matter of great theoretical interest to know whether this stage in the non-menstruating animals is actually as free from tissue breakdown as I have rather summarily indicated. In other words, is menstruation a totally peculiar affair, sharply different from what goes on in mammals generally, or is it merely an exaggeration of a degenerative process that is present but not extensive in lower animals.? This question is being investigated, but the answer cannot be given now. We need to know most of all what goes on in the uterus at the end of the corpus luteum phase in the New World monkeys (the capuchins, spider monkeys, and howler monkeys), which in spite of their close evolutionary relationship to the other primates do not menstruate externally. Here, if anywhere, we may expect to find transitional conditions that may help explain the wherefore of menstruation. The evidence is not yet in, but I may say that there are hints, apparent to the expert microscopist, that even in the rabbit and other non-menstruating mammals the retrogressive phase has an element of acute damage in it. These signs are, however, slight indeed and the statement holds true that in almost all mammals, when the corpus luteum has done its work, and the uterus is released from its phase of progestational proliferation, it
{ 163 }
THE HORMONES IN HUMAN REPRODUCTION
settles gently and inconspicuously back to the state it was in before the follicles matured.
Theories about the menstrual cycle. There is no need to discuss outmoded theories of the cycle here, except to exclude one or two ancient fallacies that still crop up occasionally. For example, some people still consider that menstruation is equivalent to estrus. This is a common notion among farmers. Because menstruation is the most prominent event in the human cycle, and estrus the most conspicuous phenomenon in the cycle of the barnyard animals, they are wrongly considered to be fundamentally alike. It would follow from this that in humans the egg is shed from the ovary at the time of menstruation, a notion which is absolutely incorrect, as will be seen from our previous discussion. Menstruation is the last stage, not the first, of the corpus luteum phase of the cycle.
Another false view, which prevailed widely among European gynecologists from 1880 to 1910, asserted that there is no chronological relation whatever between ovulation and menstruation. The egg may be shed at any stage of the cycle. This conclusion was drawn by surgeons who knew very little about other species, and who moreover usually saw at the operating table not normal pelvic organs, but those of patients with gynecological ailments, often subject to disturbances of the cycle.
When it began to be understood clearly that the ovary is an organ of internal secretion, a group of first-class German gynecologists, including especially Robert Schroeder, Robert Meyer, and Ludwig Fraenkel (the latter two now in exile) developed a theory which had been vaguely outlined a generation earlier, that the corpus luteum is in some way associated with the menstrual cycle. Gradually their views, clarified by intensive observation of human material, arranged themselves into a theory of the cycle which was very plausible and which has turned out to be partly correct.
{ 164 }
THE MENSTRUAL CTCLE
This states that menstruation is simply the downfall of the premenstrual (progestational) endometrium, and that it is caused by the degeneration of the corpus luteum. It will be seen that this theory fits all that has been said about the primate cycle thus far, and that it is compatible with our diagram. Fig. 22. According to this theory, the endometrium cannot menstruate unless it is first built up to the "premenstrual" state. Professor Meyer put this into an aphorism which was much quoted by the gynecologists "Ohne Ovulation keine Menstruation" — without ovulation there can be no menstruation.
This is a beautiful, clear hypothesis, and it is half true. It is also, unfortunately, half false. The fallacy is subtle but fundamental, and leads us headlong into a mass of unsolved problems.
Anovulatory cycles. The failure of the German theory of the cycle is a matter of especial interest to me, for it was my lot to obtain (to my great perplexity) the first undeniable evidence against it. The story is best told as it happened. In 1921, after several years of work on the cycle of the domestic pig, I felt prepared to begin a study of a menstruating animal and for this purpose I chose the Rhesus monkey. Practically nothing was known on the subject. There had been two investigations. Walter Heape, a distinguished English biologist, had gone to India more than twenty years before to study reproduction in Rhesus monkeys and langurs, but illness had forced him to return to Cambridge, where he followed and described the cycles of a few animals he had taken home with him. M. A. Van Herwerden had studied material of a wholly different kind. Hubrecht, the great embryologist of Utrecht, had collected a great many reproductive tracts (uteri with ovaries) from several species of monkeys. These had been obtained largely by Dutch colonial officers in the East Indies. Miss Van Herwerden examined these specimens, which were unaccompanied by life histories
{ 155 }
THE HORMONES IN HUMAN REPRODUCTION
or records of menstrual cycles, because the animals had been shot in the jungle by hunters. As regards the relation of menstruation to ovulation in the cycle of the monkey, the results of Heape and Van Herwerden were obscure and puzzling. Heape in his few cases observed no clear relation. Van Herwerden actually found that in some of the Hubrecht specimens the uterus was menstruating but there was no corpus luteum at all in the ovaries. In other menstruating animals a corpus luteum was present. This variability could perhaps be reconciled with the older theories of the human cycle, but not with the Meyer-Schroeder-Fraenkel theory. The absence of life histories, however, cast uncertainty upon the significance of Van Herwerden's observations. A hunter's specimen lets us see only one instant in the life of the animal ; who could tell the significance of these puzzling cases so completely removed from the context of life?
Meanwhile the German interpretation seemed plausible indeed. It could be matched without difficulty to all the recently gained knowledge of the cycles of mammals. Stockard and Papanicolaou's studies of the guinea pig (1917), those of Long and Evans on the rat (1921), which I had been privileged to watch for four years, and my own on the domestic pig had all emphasized the occurrence of regular cycles of ovulation followed by the progestational phase of the uterus. I supposed that application of the same methods to a menstruating mammal, namely the Rhesus monkey, would reveal a strictly parallel sequence, with menstruation as its last stage. If I kept my animals in good condition, observed their cycles with perfect vigilance, and autopsied them at carefully chosen stages in their cycles, I should obtain a series confirming the German theory. I thought that 25 monkeys and three years' work would suffice to establish the normal cycle, after which we could go on to all sorts of experimental studies in confidence that we could
{ lo6 }
THE MENSTRUAL CYCLE
elucidate the normal physiology and the disorders of the human menstrual cycle.
Imagine my confusion when the very first monkey we killed disagreed completely with all we had expected. Rhesus monkey No. 1 was in my colony more than a year. She had 12 menstrual cycles in 12 months, the last 5 of which were respectively of 27, 29, 25, 24, 27 days, averaging 26.4 days. In the hope of recovering a young corpus luteum and of finding an egg in the oviduct or uterus, she was killed 17 days after the onset of the last previous menstrual period and 9 days before the expected onset of the next. To our astonishment, neither ovary contained any sign of recent or impending ovulation. There was no large follicle, no recent corpus luteum, nor any older corpus luteum from the last two or three cycles. In short, this animal was undergoing cycles of menstruation without ovulation and therefore without corpora lutea.
Monkey No. 2, on the other hand, fulfilled our original expectations. She, too, had a series of regular cycles. She was killed 14 days after the onset of the last period and 12 days before the onset of the next expected period. The left ovary contained a recently ruptured follicle and the egg was in the oviduct. This, by the way, was the first egg of any primate ever recovered from the oviduct. The case fits the diagram perfectly.
To make a long story as short as possible, it turned out that Rhesus monkeys do not ovulate in every menstrual cycle.* When they do ovulate, the corpus luteum of course is formed and causes progestational (premenstrual) changes in the uterus. When the corpus luteum degenerates, typical menstruation occurs, by breakdown of the premenstrual endometrium. When the animal does not ovulate, then natu 6 George W. Corner, "Ovulation and menstruation in Macacus rhesus." Carnegie Institution of Washington, Publication No. S32 {Contributions to Embryology, vol. 15), pp. 75-101, 1923.
{ 157 }
THE HORMONES IN HUMAN REPRODUCTION
rally there is no corpus luteum and therefore no premenstrual change in the uterus. Menstruation occurs anyway, and the breakdown takes place in an endometrium which is still in the unaltered state. The corpus luteum is necessary for the premenstrual state, but not necessary for the breakdown.
This analysis of the situation has been confirmed by Markee through watching menstruation in endometrium grafted in the eye. Markee tells us that when he applies the microscope to the grafts he sees only one difference between ovulatory and anovulatory menstruation, namely the occurrence of the progestational phase in the former and its absence in the latter. The shutting off of the blood supply, the subsequent reflux of blood through the coiled arteries, the rupture of the small vessels and the hemorrhage are the same in both instances. With all this evidence it can hardly be doubted that anovulatory bleeding is also menstruation.
It is not possible to distinguish between ovulatory and anovulatory menstruation by ordinary observation of the living animals. The cycles are of similar length, the bleeding is similar in appearance and duration. Recent studies by Ines de Allende and Ephraim Shorr suggest that it may be possible in the future to detect anovulatory cycles by studying the vaginal cells.
My description of menstrual cycles without ovulation was at first rather generally mistrusted, but it has been confirmed by everyone who has studied the Rhesus monkey.^ We know that anovulatory cycles are likely to occur in young animals in the first months after the establishment of menstruation, and in fully mature females in the early fall and late spring, that is to say at the beginning and end of the active breeding season of the winter months. Rhesus monkeys do not menstruate regularly in summer. The anovulatory cycles tend
7 Carl G. Hartman, "Studies in the reproduction of the monkey, Macacus (Pithecus) rhesus." Carnegie Institution of Washington, Publication No. 433 {Contributions to Embryology, vol. 23), pp. 1-161, 1932.
{ 158 }
THE MENSTRUAL CYCLE
to occur, therefore, when the reproductive tract is preparing for its highest activity or receding from it. My papers describing the monkey cycle set off an active debate among the gynecologists as to whether anovulatory cycles occur in women. After much discussion and a great deal of careful observation, it is generally agreed that anovulatory cycles do occur, though with much less frequency than in monkeys. They seem to be most frequent in young girls and in women approaching the menopause.
There is no place for menstruation without ovulation, in the theoretical scheme which I have called the German theory. Therefore the savants who had formulated that theory simply declared that anovulatory menstruation is not menstruation at all. The rest of us, however, have gone on trying to find an explanation that fits all the facts. In this search the new knowledge of the ovarian hormones has begun to help us.
THE HORMONES AND MENSTRUATION
Experimental uterine bleeding. A simple experiment, made in 1927 by Edgar Allen, opened up the whole problem of the relation of the ovarian hormones to menstruation. Allen found that removal of both ovaries from a mature Rhesus monkey will usually cause within a few days a single period of menstruation-like bleeding. Why the medical profession had failed to discover this fact from human surgical patients is difficult to understand. It has long been known that removal of the ovaries abolishes the menstrual cycles, but the doctors had missed observing the fact that one period of hemorrhage often follows the operation before the cycles cease permanently. They seldom remove the ovaries except in the presence of disease, when the cycles are already altered, or for tumors which themselves produce bleeding, or as part of a larger operative procedure which may cause surgical hemorrhage from the uterus. Thus bleeding due purely to
{ 169 }
THE HORMONES IN HUMAN REPRODUCTION
removal of the ovaries escaped notice until Edgar Allen discovered it in monkeys.
As a matter of fact, an experiment like Allen's had once been done on humans, on a large scale, and with the best intentions in the world. Robert Battey, a surgeon of Augusta, Georgia, in 1872 conceived the idea that neuroses and insanity in women are often concerned with the ovaries and may be treated by removal of these organs. He was probably led into the notion by observation of cyclic mental disturbance, paralleling the menses, insanity following child-bearing, and other conditions in which sex and the reproductive functions were of course concerned, though in a far more complex way than he could have imagined. Battey's radical proposal to remove the normal ovaries was put forward just at the time when the surgeons had gained command of the operation of ovariotomy (as they often ungrammatically called it). Antiseptic surgery. Lister's gift to the world, was now in general use, and the great American ovariotomists Ephraim McDowell, the Atlees, and their followers in Britain and Europe had worked out the operative technique. The operation was therefore relatively safe, and no doubt the patient's mental condition was often improved or at least subdued by the surgical intervention, with its anesthesia and opiates, by the rest in bed, and the nursing and general attention. At any rate "Battey's operation" was taken up widely by a profession thoroughly baffled by mental disease. Thousands of women were subjected to this drastic operation, not only in the United States, but in England, Germany and the rest of Europe, until in good time it became obvious that the psychiatric results did not justify it and that insanity with cyclic or sexual symptoms cannot be pinned directly to the ovaries. The late Dr. Edward Mulligan of Rochester, New York, told me of an incident in the last years of Battey's operation. Dr. Mulligan when a young surgeon studied for a time, about 1883, at Bellevue Hospital in New York City
{ 160 }
THE MENSTRUAL CYCIiE
with the pathologist William H. Welch, himself a young man on his way to the Johns Hopkins and the leadership of the American medical profession. One morning Welch showed his pupils a tray containing a number of normal ovaries, removed that morning in the operating rooms, and took the occasion to denounce the practice of Battey's operation in words so vigorous that Dr. Mulligan still remembered them more than forty years afterward.
The point of all this is that removal of the normal human ovaries was very often followed within a few days by a period of bleeding from the uterus lasting several days. This appears in many of the case reports in medical journals from 1872 to 1885. The doctors did not always report all the postoperative details, but when they did they generally noted the hemorrhage, but never with comprehension. Thus an important observation was missed because the observers' minds were unprepared.
We must digress for a moment to mention that under the strict corpus luteum hypothesis of menstruation (which I have for brevity called the German theory) removal of the corpus luteum may be expected to bring on menstruation. This had been perceived and demonstrated at the operating table before 1927, when Allen announced, on the basis of his experiments on monkeys, the broader fact that removal of both ovaries, with or without a corpus luteum, has the same effect. It may help keep things clear, if we point out something the reader has probably thought out already, namely that removal of a corpus luteum produces bleeding from a premenstrual endometrium, whereas removal of the ovaries without a corpus luteum produces bleeding from an unaltered endometrium, as in anovulatory menstruation.
Estrin-deprivation bleeding. Edgar Allen reasoned that the effects of removal of the ovaries of his monkeys were really due to removal of the estrogenic hormone, which had recently been discovered, thanks so largely to his own in { 101 }
THE HORMONES IN HUMAN REPRODUCTION
vestigations. He therefore took a castrated female monkey and gave her a course of injections of estrogenic hormone. When he discontinued the treatment, bleeding ensued. In other experiments he removed the ovaries and immediately began daily doses of estrogenic hormone. As long as the hormone was given, there was no bleeding; that is to say, the hormone was able to substitute for the ovary. When it was discontinued, the bleeding occurred.
The following diagram represents graphically the experiments just described.
Removal of ovaries; estrin deprivaiion:
ovaries removgd^ ^.f^j-Zil^J^^^""^
INTACT ANIMAL CASTRATE ANIMAL \
ovAries rg-moved-^^ i^^-estrin ^iven--^
INTACT
C AST RATE \
Fio. 24. Illustrating the experiments of Edgar Allen, 1927, 1928. In this and the following 3 graphs the black bars indicate uterine bleeding. These diagrams are from an article by the author in the American Journal of Obstetrics and Gynecology, by courtesy of the C. V. Mosby Company.
On this basis Allen formulated the estrin-deprivation hypothesis of menstruation, which suggests that natural menstruation, like the experimental bleeding, is due to a cyclic reduction of the amount of the estrogenic hormone available in the body.
Subsequent experiments done with carefully graded doses of the hormone, including especially those of Zuckerman, of Oxford, have shown that not only total deprivation, but also
{ 162 }
THE MENSTRUAL CYCLE
mere lowering of estrogen dosage below a certain level will produce the bleeding. The word "deprivation," as used in this connection, is therefore to be taken in a relative sense.
Estrin- deprivation hijpothjesia:
INTACT ANH^MAL /
^ >^
Teat of the hijpothesia:
__ est Trm_siyerv2r INTACT ^"^ ^/__ "^ \ no bleeding
- ^ ^^,5 J- ^ - -^ ^ X Xr-X X X K
Fio. 25. In the lower figure the natural level of estrogen is shown fluctuating cyclically, not as a proved fact, but to show how the actual results of injecting the ovarian hormone bear on the estrin-deprivation theory.
The correctness of the estrin-deprivation h3^othesis can be tested in a very simple way. We need only choose a monkey that is menstruating regularly, and keep up her estrogen level by injecting the hormone, for say ten days before the expected menstrual period. This should prevent menstruation. I tried this in a sufficient number of monkeys, giving them doses of estrogen I thought similar to their own natural supply from their ovaries. Later in the experiments these doses were increased several fold. The hormone did not stop the next menstrual period. If the treatment was continued into later cycles, menstruation was often delayed, perhaps because of roundabout action through the pituitary gland. Zondek has found that in women very large doses of estrogenic hormone disturb the menstrual cycle, owing to inhibi { 163 }
THE HORMONES IN HUMAN REPRODUCTION
tion of the gonadotrophic mechanism of the pituitary. These upsets produced with long-continued or very large doses are however not altogether pertinent. The theory calls for relatively small fluctuations, within the body's normal range of hormone production. On this hypothesis, however, the very first period should be prevented, and this did not occur. If my dosage of hormone was really physiological, as we say (that is, something like the amount the animal herself would produce) then the cstrin-deprivation hypothesis in its simple original form is not adequate to explain the observed facts.
Progesterone and menstruation. On the other hand, administration of the corpus luteum hormone even in small doses prevents menstruation in experimental animals, abolishing the very first menstrual period after injections are begun (provided they are started a few days before the expected onset). Both Hisaw and I have found that experimental estrin-deprivation bleeding, produced by removal of the ovaries or by discontinuance of a course of treatment with estrogenic hormone, is prevented by small doses of progesterone. Smith, Engle and Shelesnyak at Columbia University arranged an exceedingly vigorous condition of estrin deprivation. Their monkeys were first given a course of gonadotrophic hormone from the pituitary gland (see p. 141) to stimulate the output of estrogenic hormone from the ovaries. They were also given generous doses of estrogens for good measure. These hormones were suddenly discontinued and at the same time the ovaries were removed. In the face of all these reasons for deprivation bleeding, modest doses of progestin (crude progesterone) completely prevented hemorrhage.
On the other hand, progesterone deprivation, like estrin deprivation, invariably causes menstruation-like bleeding. This was very clearly apparent in a series of my experiments in which progesterone was given to normally menstruating monkeys. During the injections, menstruation ceased. When
{ 164 }
THE MENSTRUAL CYCLE
Progesterone preventa eetrin-deprivaLLion bleeding:
ovAT?ie0 present /pros-e^lLn ^ eslriti^iven ic ^iven V
-^ — X X. X X
withcLrdLWTn. — ^ , , t ^ \ "nobleedm^
I NTACT CA5^RATE
\
o bleeding N \^
v^7^ r JS^
CA5TRATE V^^ >^
Fio. 26. The upper figure illustrates the experiments of Smith and Engle, 1932, and Engle, Smith and Shelesnyak, 1935. The lower figure represents the results of Hisaw, 1935, and Corner, 1938. Estrin-deprivation bleeding is postponed by progesterone; discontinuance of progesterone is then followed by bleeding.
the hormone was purposely stopped at a time which would have been midway between two periods (had the latter been occurring on their original schedule) progesterone-deprivation bleeding then occurred within a few days. The monkey next menstruated spontaneously about 4 weeks after the experimental period. This tells us that the monkey's timepiece mechanism accepts progesterone-deprivation bleeding as if it were actual menstruation, and takes a fresh start from the induced period.
The diagram (Fig. 26) illustrates these facts.
At this point Dr. Markee may be called again as a witness. He tells us that when bleeding is produced in one of his
i 165 }
THE HORMONES IN HUMAN REPRODUCTION
eye-grafts, by withdrawal of either the estrogenic hormone or progesterone, he observes the same sequence of blanching and hemorrhage that occurs in spontaneous menstruation. If the monkey is given progesterone, the graft will bleed from a "premenstrual" state; if given estrogenic hormone, it bleeds from the interval state.
With this information in hand it is possible to plan an experiment in imitation of the normal ovulatory cycle. This is represented in the upper half of the following diagram, Fig. 27. The underlying idea occurred to workers in the Oxford, Harvard, and Rochester (N.Y.) laboratories at
Progesterone during a. courae of estrin:
I estrin I 500 Inl.U.
cslrinl25Int.U. progesterone Im^. i ^^
deiilij dadlv -^ ?tz"^r:2i~z?-'zr^irTi2i !
\
\ bleeding
CASTRATE X
Currenl: hijpothesis of ovulalorij incnslruation:
corpus luteum rclro^ressca n -progesterone acting —^ J X — X — X — x — X — »t — ^ — y^
resenrioQcL \
effective on enxioimetri-u-na
INTACT
\
-- inetfective
V
\
^•-^
Fig. 27. The upper figure illustrates the production of bleeding after discontinuance of a course of progesterone, in spite of continued and more intensive estrogen treatment. The dosage shown is that of the author's experiments (Corner, 1937, 1938) ; similar results were obtained by Zuckerman, 1937, and by Hisaw and Greep, 1938.
{ 166 }
THE MENSTRUAL CYCLE
practically the same time, and gave consistent results when tried. The dosage cited here is that of my own version of the experiment. A castrate female monkey is given a daily dose of estrogenic hormone, 125 international units, sufficient to build up the endometrium to normal thickness and structure. After 10 days, a daily dose of progesterone is added (just as would have happened had the animal developed a corpus luteum of her own). Ten days later, at the 20th day of the experiment, the progesterone is discontinued, but the daily injection of estrogenic hormone is continued. In spite of the estrogen, we find that bleeding invariably occurs in a few days. Indeed, the dose of estrogen may be greatly increased, say to 500 international units, beginning on the day on which the progesterone is discontinued ; but menstruation-like bleeding still occurs. Seven hundred units or more may be necessary to prevent it, although such doses as 500 or 700 international units are of course much more than necessary to maintain the uterus when not working against progesterone deprivation.
These facts enable us to construct a relatively simple hjrpothesis of the menstrual cycle which is really a modified form of the estrin-deprivation hypothesis (Fig. 27, lower part). We start by assuming that progesterone in some way or other has the property of suppressing the menstruationpreventing power of estrogen, while itself holding off menstruation. In the normal cycle the animal does not bleed in the first half of the cycle (follicular phase), because the ovaries are furnishing estrogen. She will not bleed during the second half of the cycle (corpus luteum phase) because the corpus luteum is furnishing progesterone. By our assumption, however, the corpus luteum is suppressing the protective effect of the estrogen; therefore when the corpus luteum undergoes retrogression, the animal finds itself deprived of the action of both estrogen and progesterone, and the en { 167 }
THE HORMONES IN HUMAN REPRODUCTION
dometrium breaks down. Ovulatory menstruation is thus a special case of estrin-deprivation bleeding.
This explanation of the normal cycle is, of course, simply a hypothesis which has been formulated to explain our observations. Whether things happen this way in the normal monkey or in woman remains to be proved. It is at least not contradicted by any of the known facts, and it has the merit of simplicity, because it calls for a cyclic variation in only one hormone, namely progesterone. Its one unproved assumption, that progesterone somehow cuts down the action of estrogen on the uterus, is supported by various other evidences of a sort of antagonism between the two hormones in some of their other activities. It has been suggested that progesterone has the property of speeding the elimination of estrogens from the body. If this proves correct it is all we need to complete our hypothesis.
This scheme does not explain anovulatory menstruation, for in cycles without ovulation there is, of course, no coming and going of the corpus luteum. Anovulatory menstruation is therefore probably due to estrin-deprivation alone. We can imitate it perfectly in castrate animals by simply giving a course of estrogen injections interrupted or sharply reduced at suitable intervals. What is actually happening in the female organism remains to be worked out. We are not yet sure that there is an actual up-and-down of estrogen in the body sufficient to produce deprivation bleeding. The daily assay of estrogens in the blood is very expensive and at present not reliable enough for our purpose. Zuckerman has shown that when a castrate monkey is kept on a relatively small but constant daily dose of estrogen, there is a tendency to occasional uterine bleeding which may become fairly regular. We may conjecture, on this basis, that perhaps some sort of give-and-take relation exists between estrogen and some other hormone, just as between estrogen and progesterone when the corpus luteum is present, so that
{ 168 }
THE MENSTRUAL CYCLE
even without the corpus luteum a periodic state of estrin deprivation occurs. Can it even be that the adrenal gland produces something that can suppress the estrogens (we know that a number of steroidal compounds resembling progesterone are extractable from that gland) ? The play of hormones in anovulatory menstruation is anybody's guess, and those of us who have worked on it can assure our colleagues, on the basis of much vain conjecture and many futile experiments of our own, that the problem is not an easy one. Some little fact is lurking just beyond our grasp.
Since the first draft of this chapter was written, Hisaw has reported from the Harvard zoological laboratory some experiments which show that very small doses of progesterone given and then discontinued (1 milligram a day, for one to five days) will set off menstruation-like bleeding in castrate monkeys which are receiving large daily quantities of estrogenic hormone. He suggests therefore that anovulatory menstruation may be due to progesterone deprivation; even if there is no corpus luteum, he says, there may be a little progesterone produced in Graafian follicles (there is, in fact some collateral evidence for this latter part of the conjecture) and this may be enough to cause menstruation when such a secretion of progesterone ceases. It is a plausible conjecture, and one which calls for no new factor outside the ovary ; but it will be difficult to prove.
The immediate cause of the menstrual process. From the foregoing sections it will be perfectly clear that the breakdown and hemorrhage of menstruation are consequent to the deprivation of estrogenic hormone or progesterone. It is also very probable, from the studies of Markee, that these effects are initiated by constriction of the peculiar coiled arteries of the endometrium, which produces damage to the tissues and ultimate degeneration. But how can it be that a temporary deprivation of one of these two particular hormones can shut off the arteries in one particular tissue.
{ 169 }
THE HORMONES IN HUMAN REPRODUCTION
This question is now the key problem in the theory of menstruation, and it remains unsolved. The attack upon it is in the stage of skirmishing, in which all the possible explanations are being put forward for discussion and trial ; but up to the present no one of them has found support by experiment. The reader may, however, be interested in the mental processes of a group of puzzled investigators, and therefore I list the conjectures for what they are worth. To merit consideration at all, any explanation must fit the facts that (a) hormone withdrawal causes uterine bleeding; (b) this does not take place at once, but only after 3 to 8 days; (c) the bleeding, once hormone deprivation is well under way, cannot be postponed by renewed injections of estrogen or progesterone; (d) it takes place in grafted bits of endometrium (in the eye or elsewhere) which have no connection with the nervous system.
Since all of these conjectures involve the arteries, it may be helpful to recall the fact that the walls of an artery contain numerous cells of involuntary muscle, laid on in circular fashion around the inner tube (endothelium) that conducts the blood. When these muscle fibers contract, they squeeze down upon the blood stream like a man's fingers abput a rubber bulb. It is thus that the blood pressure is raised by a dose of adrenin or by a strong emotional state, both of which cause the arterial muscle cells to contract. Such muscular cells exist in the coiled arteries of the uterus as in all other arteries (Appendix II, note 13).
Hypothesis 1. It may be that the coiled arteries are peculiarly and directly dependent upon the ovarian hormones, in some such way (for example) as the ovary is dependent upon the pituitary. This means that withdrawal of the ovarian hormones would let down the condition of the coiled arteries, causing them to contract. This hypothesis is the simplest, calling for no other hormones or special substances, but it is exceedingly difficult to try out, for the only
{ 170 }
THE MENSTRUAL CYCLE
way of proving that the ovarian hormones are the sole factors involved is to exclude all other possible factors, but when we cut off the estrogenic hormone, how can we know we are not thereby putting some other factor into action? If somebody could show us how to keep a coiled artery alive and working outside the body where we could deal with it alone, we could soon test this hypothesis, but the infant art of tissue culture has by no means reached the point of keeping an artery alive all by itself, and moreover these arteries are so tiny that they would have to be handled under the microscope — a truly difficult project!
Hypothesis 2. This admits the possibility, mentioned above, that withdrawal of estrogen permits something else to go into action. We know that even in the non-menstruating animals, withdrawal of the ovarian hormone causes a certain amount of deterioration of some of the cells of the surface epithelium and of the glands of the uterus. Under the microscope we see fragmentation of the nuclei and the accumulation of protoplasmic debris in the cell bodies. Is it possible that some chemical substance produced in the course of cellular breakdown (as histamine, for instance, is produced in burned tissues) diffuses through the endometrium to the arteries and causes them to contract? This hypothesis has interested me very much and I have made many experiments to test it, but always with negative results.
Hypothesis S. Another conjecture, a variation upon the foregoing, is that the uterine coiled arteries are sensitive, when not protected by the ovarian hormones, to some substance that is normally present in the blood stream. We must suppose that withdrawal of the hormone allows this substance to act upon the arteries. One of the possible constrictor substances would be pituitrin, the secretion of the posterior lobe of the pituitary gland, a hormone which is highly potent in promoting contraction of smooth muscle. Carl G. Hartman tried this with negative results, and moreover P. E. Smith
{ 171 }
THE HORMONES IN HUM AN REPRODUCTION
obtained bleeding by estrin deprivation in monkeys from which he had removed the whole pituitary gland. Adrenin has been thought of, but Edgar Allen succeeded in producing estrin-deprivation bleeding in monkeys from which the adrenal glands had been removed. This experiment is not quite conclusive, for monkeys may possibly have other sources of adrenin beside the adrenal gland. Up to the present, at least, this hypothesis has yielded no valuable clues.
Hypothesis 4. George Van S. Smith and 0. W. Smith have suggested that the bleeding of menstruation is caused by conversion of estrogenic hormone into a non-estrogenic byproduct which is toxic to the endometrium. This hypothesis could perhaps explain ovulatory cycles, but it cannot be fitted very well to simple estrin-deprivation bleeding; in any case it will be acceptable only when somebody comes forward with chemical derivatives of the estrogenic hormones that are especially toxic to the endometrium (Appendix II, note 14).
These are the most plausible current guesses about the immediate cause of uterine bleeding after hormone deprivation. None of them has been proved or even rendered likely, by experiment. It is indeed vexatious that we cannot clear up this important problem.
The modern concept of the cycle. By way of summary, let us now set forth a concise description of the primate cycle as revealed by recent research. What follows will, I think, be accepted by most of the American investigators, and also the British, although a die-hard English gynecologist a few years ago dubbed it "the American theory."
We begin by suggesting that there is a basic tendency to cyclical function of the ovaries, and that this is produced by a sort of reciprocal "push-pull" reaction between the pituitary and the ovarian hormones, as explained in full earlier in this chapter. In most cycles of fully mature human females, the pituitary gonadotropic hormones cause the ripening of
( 172 }
THE MENSTRUAL CYCLE
a Graafian follicle, the discharge of its egg, and the formation of a corpus luteum. This in turn sets up the progestational or "premenstrual" state of the endometrium. When the corpus luteum degenerates, menstruation ensues because of the withdrawal of progesterone. In some cycles, however, especially in young girls and in women approaching the menopause, a follicle does not ripen in the ovary, but after about the same interval as in an ovulatory cycle, namely 4 weeks, some process not yet understood leads to reduced action of estrogenic hormone, and bleeding ensues which we call anovulatory menstruation.
This view of the cycle requires, of course, much more investigation before we shall be able to understand the whole process; I have already pointed out the larger gaps in our knowledge. It certainly represents a great advance toward the truth; and what is indeed important, it gives us a far clearer and more hopeful viewpoint about the disorders of menstruation than do older concepts of the cycle. Since menstrual bleeding is caused by fluctuation in levels of the ovarian hormones, it follows that noncyclic, pathological bleeding, such as occurs in excessive and irregular periods may also be caused by abnormalities in amount proportion, or kind of these hormones. We must consider that there are not two sharply distinct kinds of functional bleeding, one being normal menstruation and the other abnormal hemorrhage. On the contrary, the modern hypothesis tells us that we must expect a series of types of hemorrhage ranging from normal menstruation through every grade of disturbance to the most severe disorder of the cycle. Gynecologists are already beginning to study and treat these distressing and difficult conditions in the light of this concept, and we may well hope these same hormones that control the normal cycle will help us to control its aberrations and at last to banish the specter of uterine hemorrhagic disease.
{ 173 }
THE HORMONES IN HUMAN REPRODUCTION
THE UNKNOWN SIGNIFICANCE OF MENSTRUATION
In all this discussion of the nature and the course of menstruation, we have had nothing to say about the significance and possible usefulness of the periodic breakdown and hemorrhage. The human mind has an intractable desire that natural phenomena shall be useful. We are not comfortable in the presence of useless or undirected activity. Menstruation in particular ought to have a practical reason for its occurrence, for otherwise it seems a totally wasteful, destructive, and vexatious business. Up to the present, however, no one has been able to demonstrate such a meaning. There are in fact only two guesses that are even worth talking about.
The late Walter Heape of Cambridge, England, one of the pioneers in the study of the reproductive cycle, proposed in 1900 that menstruation is the same thing as a period of bleeding that occurs in female dogs when they are going into heat, i.e. in the week preceding ovulation. A somewhat similar proestrous bleeding occurs in cows, particularly in heifers. Such bleeding is easily explained, for it is clearly due to engorgement of the blood vessels produced by a strong action of the estrogenic hormone. Under the microscope it does not resemble menstruation ; the blood oozes from superficial blood vessels and there is little or no breakdown of the tissues. When Heape wrote, nothing was known of the time of ovulation in the primate cycle, nor of the premenstrual endometrium and its dependence upon the corpus luteum. In the primates, on his theory, ovulation would be expected to occur during menstruation, or immediately after the flow, just as in the bitch and cow ovulation occurs about the end of the proestrous bleeding. Since we know now that ovulation takes place a week to ten days after the cessation of menstruation, we can reconcile Heape's theory with the facts only by supposing that in the menstruating primates there is first proestrous bleeding, then a delay unknown in the other animals, and
{ lU }
THE MENSTRUAL CYCLE
finally ovulation. This theory, and one or two ingenious variations upon the same theme by later English writers, F. H. A. Marshall and Zuckerman, all seem too complex to be probable, and moreover they suffer from a very serious objection. Unlike the menstruation-like bleeding, which can be produced in monkeys and women by withdrawing estrogenic hormone, the proestrous bleeding of dogs is produced by building up the level of estrogenic hormone, as was shown by R. K. Meyer and Seiichi Saiki in our Rochester laboratory in 1931.
A few years ago, Carl G. Hartman discovered that in Rhesus monkeys there is almost always a slight bleeding from the uterus about the time of ovulation. This does not show externally and is discernible only by applying the microscope to washings of the vagina. Sections of the uterus made at this time reveal that a few red blood cells are escaping from superficial capillary blood vessels of the endometrium, which are engorged by the action of the estrogenic hormone. In the laboratories we call this slight bleeding "Hartman's sign" and take it as evidence that there is a ripe follicle in the ovary. This is the actual equivalent of Heape's proestrous bleeding. It has since been found to occur in women, though probably not as regularly as in monkeys. These observations prove clearly that menstruation is something else than proestrous bleeding.
Hartman has proposed another explanation for menstruation. He points to the fact that in many mammals, at the time of implantation of the embryo, the uterine secretion contains red blood cells. He tells us also that in many viviparous animals lower than the mammals, for example certain salamanders and fish, in which the embryo depends upon the maternal tissues for nourishment, bleeding in one form or another usually occurs into the brood chamber. Hartman compares menstruation to bleeding of this kind and conjectures that it is simply a means of getting the vitally useful blood pigment, hemoglobin, into the region where the early
{ 176 }
THE HORMONES IN HUMAN REPRODUCTION
embryo is to reside. We have to suppose that if in any given cycle an egg is fertilized, the premenstrual changes go to the very verge of menstruation, letting a little blood out of the vessels into the tissues to enrich the implantation site for the embryo. Since, however, a "missed period" is the first sign of beginning pregnancy, we must also suppose that attachment of the embryo then stops the process before external hemorrhage occurs, and even before there is any significant breakdown of the endometrium. If there is no embryo, the breakdown goes all the way. This is a very interesting conjecture, for it assigns a necessary and worthy function to the strange flux of menstruation. Careful study, however, of the uterine lining of the monkey just before and during implantation of the embryo, and of the very few human specimens during early implantation that are as yet available, does not support this hypothesis, for they do not show beginning hemorrhage in the endometrium. We know that many other mammals succeed in implanting their embryos without any such provision of free blood or hemoglobin in the endometrium; and we know also that sometimes in women and often in Rhesus monkeys menstruation occurs in anovulatory cycles, when there can be no embryos to profit by it. This hints that perhaps the process of menstruation evolved without reference to the embryo.
Menstruation, then, is still a paradox and a puzzle — a normal function that displays itself by destruction of tissues ; a phenomenon seemingly useless and even retrogressive, that exists only in the higher animals ; an unexplained turmoil in the otherwise serenely coordinated process of uterine function.
"I often say that when you can measure what you are speaking about and express it in numbers you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science." - Lord Kelvin, in Popular Lectures and Addresses, lecture on Electrical Units of Measurement, 1883.
Chapter VII Endocrine Arithmetic
HOW much of a given hormone is found in the body at one time? How much is produced in a day? How much is found in the gland at one time ? What is the output of a single cell? These are questions to which we must have an answer if we want to understand the glands of internal secretion and use our knowledge for the benefit of mankind. Certainly every merchant must have this kind of information about his stock in trade, and the manufacturer about his materials and his product. The science of endocrinology is, however, a long way from any such basis for calculation. How can we measure the output of a factory (i.e. an endocrine gland) when we do not know exactly what raw materials it uses, how it makes the product, or what becomes of the product when it is used? In the case of most of these chemical factories we do not even know the capacity of the manufacturing plant. The insulin factory, for example, consists of many thousand bits of tissue, the pancreatic islets, irregular in size and shape, scattered through the pancreas. In the pituitary, although the gland is measurable as a whole, we do not know what particular cells are associated with the various hormones made in the gland, nor even indeed just how many hormones it produces. So it goes throughout this puzzling system of glands. We are dealing at present largely with unmeasurable organs and with incalculable processes. We are able only to appreciate some of the end results, not the fundamental steps. To measure and calculate what is going on within the glands and thus to understand the chemical reactions and strike the balance of input and outgo — that task lies ahead.
{ 179 }
THE HORMONES IN HUMAN REPRODUCTION
RATE OF SECRETION OF THE CORPUS LUTEUM HORMONE
It happens that of all the endocrine glands, the corpus luteum is the one with which we can go farthest at present toward calculating the answers to the questions with which this chapter opens. The amount of glandular tissue can be ascertained, for it occurs in discrete masses of more or less spherical form and is composed of cells which can be measured and even counted with a fair degree of accuracy. The chemical structure and molecular weight of the hormone are fully known, and the dose necessary to produce certain definite effects is known. With these data at hand, let us take pencil and paper and see how far we can get.
The following calculations are of course approximate, not precise. They represent a preliminary exploration in a brand new field of study. There are unavoidable flaws in our procedure. In our arithmetical operations, for instance, we shall have to combine figures obtained from observations on rabbits with others learned from swine, thus violating one of the primary-grade rules of arithmetic, picturesquely stated long ago by one of my teachers, "You can't add cows and horses." Some other uncertainties will appear as we go along. If our results come out anywhere between 50 per cent and 200 per cent of the true figures we shall be doing very well for a start. Physicians who have to decide on the dosage of ovarian hormones for their patients will be glad to have even that; and as for my lay readers, they may at least fmd this chapter amusing. At any rate, when I presented some of these calculations at the Cold Spring Harbor Symposium on Quantitative Biology in 1937, that earnest little assembly of research men surprised itself — and me — by being very much amused, partly perhaps because it really was funny to see a medical man so gaily slip the leash and wander down a strange pathway, and partly because of the incongruity between our simple experi { 180 }
ENDOCRINE ARITHMETIC
ments on rabbits and sows, and the final emergence into pure theory in terms of molecules by the billion. Toward the end of my discourse, however, the hearers settled down and discussed the calculation quite seriously. Our chairman, in fact, sat up all the next night figuring on a furtiier stage of the investigation, and in the morning, weary but still enthusiastic, brought me several more pages of arithmetic. What follows here is the substance of that presentation, revised in consideration of some facts contributed in discussion by members of the symposium, and corrected also in the light of subsequent knowledge.
1. How much progesterone is produced daily by a given amount of corpus luteum tissue? We begin by considering the fundamental property of the corpus luteum, namely, to produce progestational proliferation of the lining of the uterus (Chapter V, page 107 and Plate XVII, B), This has been studied chiefly in the rabbit, in which species it shows up with especial clearness. In a rabbit there are, of course, several corpora lutea at a time. By cutting down their number by surgical operation on the ovaries under anesthesia, it is possible to ascertain the minimum number of corpora lutea necessary to produce full progestational proliferation as in figure D of Plate XVIII.
(a) A young Frenchman, Joublot, the first to try such an experiment (1927), found that two corpora lutea were sufficient, but one was insufficient. I tried it also, and found that one corpus was sufficient, but half a corpus insufficient. Lucien Brouha, then in Belgium (1934), found one or two corpora lutea necessary. In our calculations we shall take the average of these three results and start with the assumption that in the rabbit one corpus luteum produces just sufficient progesterone to cause typical eff'ects upon the lining of the uterus.
(b) To produce the same effect with progesterone, giving one injection per day, requires about 0.2 milligrams daily. Dr. Pincus reports that by giving the hormone in two injec { 181 }
THE HORMONES IN HUMAN REPRODUCTION
tions, the dail}' dose can be brought down to about 0.13 mg. Let us take this lower figure as the basis for subsequent calculations. It may help to visualize the quantities we are discussing if we remind ourselves again that an ordinary postage stamp weighs 60 milligrams.
From (a) and (b) we may conclude that one corpus luteum produces about 0.13 mg. of progesterone daily. Here we are making another assumption, namely that the progesterone we administer in oily solution is utilized by the rabbit as efficiently as she can utilize the progesterone she makes in her own ovaries. This is really not impossible, for only very small amounts of oil are used and they are slowly but completely absorbed. This point will be discussed again later when we attempt to calculate the rate of output of estrogenic hormone.
Our calculation can be checked roughly by considering another action of progesterone, namely the maintenance of pregnancy in the rabbit. This requires more of the hormone. Brouha found that to preserve pregnancy to the 8th day, the rabbit must have three or more corpora lutea (instead of merely the one corpus luteum required to produce typical changes in the uterus). If we want to maintain pregnancy with progesterone after removal of the ovaries, we must also increase the dose something like 3 times or more. Willard Allen found 0.5 to 1.0 mg. of progesterone daily to be the necessary dose. In this sort of experiment we find therefore that one corpus luteum provides the equivalent of 0.16 to 0.33 mg. of progesterone daily, a figure in crude agreement, at least, with that of 0.13 mg. arrived at previously.
The volume of tissue in a rabbit's corpus luteum is approximately 3.25 cubic millimeters. Dividing this into the daily output of 0.13 mg., we get the answer to question 1: One milligram of rahhifs corpus luteum produces about O.O4 milligram of progesterone daily,
{ 182 }
ENDOCRINE ARITHMETIC
2. How much progesterone is made daily in the ovaries of one rabbit? Although the number of eggs shed by a rabbit at one time, and hence the number of corpora lutea in one crop, varies from 1 to 18, the number occurring most frequently (modal number) is 8. Eight corpora lutea multiplied by 3.25 (the volume of one corpus luteum in cubic millimeters) and then by 0.04 (the output of progesterone, in milligrams, by one milligram of corpus luteum) gives the answer to question 2: The modal daily output of progesterone by the ovaries of one rabbit is about 1.04 milligrams^ and the range is from 0.13 mg. when only one corpus luteum is present, to 2.3 mg. with the maximum number of corpora lutea, namely 18.
3. How much progesterone is produced daily by the ovaries of a sow? This is important to know because the sow is the source of most of the natural progesterone that has been extracted and the only animal in which we know the amount that is present in the ovaries at any one time. The volume of one corpus luteum of the sow is approximately 625 cu. mm., the equivalent of 160 rabbit corpora lutea. Assuming that the corpora lutea of the two species are equally efficient, volume for volume, and therefore that the amount of progesterone produced in each is directly proportional to the amount of glandular tissue (an assumption for which at present there is no evidence) then 1 corpus luteum of the sow would produce 21 mg. of progesterone daily.
In a sow possessing the modal number of corpora lutea, which is 10 in that species, the total daily output of progesterone would be 210 mg. per day. The range would be from 21 mg. when one corpus luteum is present to 525 mg. with the maximum recorded number of corpora lutea in the sow, namely 25. This result seems improbably high, but since we have no present means of improving it, let us use it tentatively in answering the next question.
4. How does the daily output compare with the amount present in the ovaries at any one moment? All the corpora
( 183 }
THE HORMONES IN HUMAN REPRODUCTION
lutea in the ovaries of one sow, when the modal number is present, weigh about 5 grams. By direct extraction the yield of crude progestin is equivalent to 0.05 mg. of progesterone per gram of raw tissue. Therefore one sow having 10 corpora lutea has about 0.25 mg. progesterone in the ovaries at the moment of killing. If the total output per day, estimated in section 3 above as 210 mg., is anywhere near correct, this means that the amount present in the ovaries at any one moment is less than 2 minutes* supply. This is a very important fact, for it points to a very high rate of "turnover" of secretion in the gland. We must think of the corpus luteum as making the hormone quite rapidly, working up only a Httle at a time but putting it through very quickly.
5. What is the daily output of the human corpus luteum? The volume of secretory tissue in the human corpus luteum is very difficult to measure, since the gland has a folded wall about a large cavity filled with connective tissue, like the monkey's corpus luteum shown in Plate IX, A. Estimates which I have made by two rough methods give 450 to 500 cu. mm. as the volume of secretory tissue in one corpus luteum. This is 150 times the volume of the rabbit's corpus luteum; and assuming once more that the human corpus luteum produces progesterone at the same rate as the rabbit's, volume for volume, then the daily output of the human corpus luteum may be estimated as about 20 milligrams per day.
This calculated result seems rather high when compared with a few estimates obtained in other ways. For example, Kaulfmann in 1935 reported producing a progestational endometrium in a human patient with 50 rabbit units in 15 days. These were presumably Clauberg units, of approximately 0.4 mg. each, making the dose about 1.3 mg. daily. Assuming that this is somewhere near the minimum effective dose, and allowing for a ratio of about 1 :4, as in the rabbit (section 1 above) between the minimum daily dose for progestational proliferation and the amount necessary to carry out the real task of
{ 1S4 }
ENDOCRINE ARITHMETIC
the corpus luteum, namely maintenance of pregnancy, then the human corpus luteum would be expected to produce about 5 mg. daily. Wiesbader, Smith and Engle of Columbia University Medical School (1936) found that a certain effect of the removal of the human corpus luteum (bleeding from the uterus) cannot be prevented by substituting 0.5 mg. daily of progesterone by injection, but can be prevented by 5 mg. This suggests that 5 mg. is a quantity sufficient to produce one of the known effects of the corpus luteum, though not necessarily the full effects.
Another way of getting at this figure is through the fact that in human females, used-up progesterone leaves the body through the kidneys as sodium pregnanediol glycuronidate, as explained in Chapter V, page 120. Venning and Browne, who discovered this fact, found that if they administered a given quantity of progesterone, they could recover about half of it in the urine as the excretion product. When they collected all the pregnanediol excreted by a patient in a whole menstrual cycle, they found that the total recoverable amount was normally about 60 mg. This would mean about 120 mg. of progesterone actually produced. Since the corpus luteum is probably actively functional during about 10 days of each cycle, we arrive at an estimate of 12 mg. of progesterone produced daily. Another research group, Pratt and Stover of the Henry Ford Hospital, Detroit, obtained considerably smaller values, for their patients yielded only 2 to 3 mg. of pregnanediol daily, which we may consider to represent at the most 6 mg. of progesterone. It is known, however, that the chemical recovery of pregnanediol and estimations of corpus luteum activity based upon this method are subject to numerous errors not fully understood. It is perhaps all we should ask for, that the various estimates and calculations we have made and cited fall within limits as close as 5 and 20 milligrams per day (Appendix II, note 15).
Physicians who have used progesterone for disturbances
{ 186 }
THE HORMONES IN HUMAN REPRODUCTION
of menstruation and for threatened abortion have seldom administered more than 2 mg. per day. If (as seems credible) beneficial results have been obtained with this and even smaller dosage, we must suppose that clinical benefit may require only the redressing of a slightly disordered balance. Our calculations make it clear, however, that larger doses, of the order of 5 mg. or more, will have to be given thorough trial before the medical possibilities of this hormone are fully understood.
6. What is the progesterone output of a single cell? Returning to the rabbit's corpus luteum, it is possible to calculate approximately the output of a single cell.
The averages of a number of measurements of the diameters of individual corpus luteum cells were 0.028 x 0.028 x 0.036 mm., giving for the cell a calculated volume of 0.000015 cu. mm. Dividing this into the volume of the whole corpus luteum we get 217,000, and making due allowance for space occupied by the blood vessels we arrive at an estimate of 180,000 endocrine cells in one corpus luteum of the rabbit.
Since 180,000 cells produce 0.13 mg. progesterone per day, the daily output of otie cell is about 0.0000007 mg.
The figure at first sight seems very small, but when the number of molecules is considered the resultant expression looks like the astronomer's rather than the biologist's quantities. We get the number of molecules made by a single cell, by the following calculation. We ascertain the molecular weight of progesterone by adding the atomic weights of the elements it is made of, namely 21 atoms of carbon, 30 of hydrogen, and 2 of oxygen. The sum is 314. This is the relative weight in comparison with the atomic weight of oxygen taken as 16. Applying Avogadro's law we know that 6 x 10^' molecules^ weigh 314 grams. Dividing the latter by the former
1 In dealing with very large numbers and very small decimal fractions it is convenient to avoid writing dozens of ciphers by using exponents. Thus 100 is 102 and .01 is 10-2. 600 is 6 x 102. The figure cited above, 6 X 1028, when written in full is 6 followed by 23 zeros, or six hundred thousand billion billions.
{ 186 }
ENDOCRINE ARITHMETIC
figure, the actual weight of one molecule is 5.2 x 10"" gram. Dividing this weight into the weight of the daily output of one cell, we find that one cell produces about 1.3 x lO"-^ or 1,300,000,000,000 molecules, i.e. more than a thousand billion molecules of secretion produced in one day by one cell.
For comparison, it may be noted that in one cubic centimeter (about 1/3 of a thimbleful) of air there are about 10" molecules.
What has just been presented is to the best of my knowledge the first attempt to calculate the actual output of a single secretory cell in any organ. It is, of course, no more than a first approximation to the truth. Yet such conjectures as this, improved and extended beyond the present powers of science, are going to lead us some day to the innermost secrets of cellular life. Perhaps the reader begins to be confused by all this reckoning of enormous numbers of very small things. Perhaps, on the other hand, he has acquired an awesome sense of the complexity of the cells, each one of them an island universe, a frail microscopic enclosure within which arise whirling billions of molecules, themselves in turn complex frameworks of latticed atoms. Upon the correct behavior of these fantastic congeries of particles in the corpus luteum each one of us depended for life itself when we were embryos ; so did all our mammalian ancestors and so will our descendants forever.
QUANTITATIVE ASPECTS OF THE RECEPTOR ORGAN We can get a further glimpse of the workings of the corpus luteum by doing a little figuring about the receptor organ, that is to say the uterus, which receives the progesterone and is affected by it.
As we have seen (Chapter V) the corpus luteum acts upon the epithelial cells which cover the inner surface of the uterus and dip down to form the uterine glands. It is the growth and multiplication of these cells which constitute the progesta { 187 )
THE HORMONES IN HUMAN REPRODUCTION
tional proliferation by which the early embryos are nourished and implanted.
From a count of the epithelial cells in sections of the uterus, I estimate that a rabbit's uterus contains (in the two horns) about 100,000,000 epithelial cells. This means that each of the 180,000 epithelial cells in a corpus luteum can affect about 500 epithelial cells. The corpus luteum cells are, however, about 25 to 50 times as large (in volume) as the epithelial cells, and therefore each of the former takes care of about 10 to 20 times its volume of the latter at the start of progestational proliferation. The disproportion is not quite so great if we calculate on the basis of the amount of corpus luteum tissue to maintain pregnancy, not merely to induce progestational proliferation. On this basis one corpus luteum cell controls at first about 3 to 5 times its volume of epithelial cells. By the time the effect is complete, the number of epithelial cells has increased a great deal, and thereafter the corpus luteum cell must maintain more of them. This means that small amounts of progesterone stir up a proportionately large effect in the uterus. That sort of trigger-like action ("You push the button, we do the rest") is characteristic of the internal secretions. It is necessary to suppose that some sort of chemical reaction between the hormone and something in the cells of the uterus starts a chain of secondary reactions which profoundly change the physiology of the uterine lining. We might have a better idea of what actually happens if we could know how much progesterone actually reaches each epithelial cell; but this cannot be calculated, because we do not know what proportion of the hormone is diverted to other receptors (the uterine muscle, the mammary gland cells, and possibly other tissues). If all of it went to the epithelial cells of the uterus, each such cell would receive daily about 1.3 x 10"* milligrams. This is almost 10^^ molecules. The actual share received must be considerably smaller.
{ 1S8 }
ENDOCRINE ARITHMETIC
THE RATE OF SECRETION OF ESTROGENIC HORMONE
It is not possible at present to estimate the rate of secretion of estrogenic hormone with anything like the fullness and probability with which such an estimate could be made regarding the corpus luteum. As pointed out in Chapter III, the cells which produce the estrogenic hormone are probably scattered throughout the ovary in the walls of small and large follicles. The number and the total volume of these cells is obviously not subject to computation, and therefore the best we can do is to estimate the activity of the ovaries as a whole. I shall give here a summary of such an estimation which was published recently in more technical form elsewhere. As in the case of the corpus luteum, we get our answer by finding out how much of the hormone we need to administer in order to restore one or another of the functional effects of the ovaries after they have been removed.
How much estrogen is required daily by the monkey? As described in Chapter VI, removal of the ovaries of the Rhesus monkey causes menstruation-like bleeding from the uterus due to removal of the source of estrogenic hormone. If we take out the ovaries and then administer estrogenic hormone, we can try various doses and discover how much we have to give to prevent bleeding. This amount will represent the replacement of the hormone formerly produced by the ovaries when they were present. In my notebooks there are records of twelve experiments of this kind which are suitable for our present consideration. In each of them the animals received 125 international units of estrone daily, beginning the day the ovaries were removed. Of these, 4 bled from the uterus beginning on various days from the 3d to the 14th after the operation, in spite of the treatment with estrone. Seven did not bleed at all during the 15 days of the experiment. One, which received a larger dose of estrone, namely 500 international units, showed
{ lli9 }
THE HORMONES IN HUMAN REPRODUCTION
a few red blood cells from time to time, beginning on the 3d day, but no external bleeding. The experiment shows that 125 international units of estrone will substitute in many cases, but not in all, for the natural product of the animal's own ovaries, as tested by the prevention of postcastration bleeding. A somewhat larger dose would obviously be required to prevent such bleeding in every case.
A variation of this experiment is to give castrated female monkeys large doses of estrogenic hormone and then drop the dosage until bleeding sets in. A number of such experiments were reported by S. Zuckerman of Oxford, England, in 1936. This investigator found that whenever he reduced the daily dose from several hundred or several thousand international units to any amount below 200 international units, estrindeprivation bleeding occurred thereafter. With more than 200 international units daily no bleeding occurred.
These observations suggest that the output of estrogenic hormone from the normal ovaries, which is of course sufficient to prevent estrin-deprivation bleeding, may be about 150 or 200 international units.
A third means of estimating the probable amount of estrogenic hormone produced by the monkey is provided by the fact that the so-called sex skin (the red swollen areas of the rump and thighs) is under the control of the hormone. Removal of the ovaries leads to shrinkage and pallor of the sex skin, whereas administration of an estrogen in sufficient amount will within a few days restore the color of this region. One of my animals, a young adult, had its ovaries removed at a time when its sex skin was in exceedingly florid condition. The whole area over the rump, the back of the thighs, and the ventral side of the base of the tail was swollen, thrown into distinct ridges and deep red in color. After the operation, but on the same day, the color and swelling were slightly reduced, owing no doubt to the stress of the operation. One hundred twenty-five international units of estrone was given daily
{ 190 }
ENDOCRINE ARITHMETIC
beginning on the day of operation. A slight but definite decrease in the color of the sex skin took place during the next 10 days. The swelling of this region diminished also, although not to the same extent as the color, and on the 10th day, in spite of the administration of estrone, external vaginal bleeding began.
From the facts that the condition of the sex skin retrogressed very slowly and external bleeding did not begin until the 10th day, that is to say later than if the animal had been given no estrogen at all, it seems that the dose of 125 international units daily was almost but not quite sufficient to maintain the animal in the same condition as before removal of the ovaries. We may estimate therefore that 150 or 200 international units would have been required to substitute completely for the ovaries.
Another method of arriving at the desired information depends upon the fact that effective action of progesterone upon the endometrium to produce the progestational ("premenstrual") condition in castrated female monkeys requires that an estrogenic hormone be administered in conjunction with the hormone of the corpus luteum. Engle of Columbia University (1937) stated that a satisfactory combination for the castrated Rhesus monkey is 30 AUen-Doisy rat units of estrone (this is approximately 150 international units) daily with 0.5 Corner- Allen unit of progesterone (approximately 0.5 milligram). Hisaw and Greep (1938) gave a similar figure, i.e. about 150 international units of estrogen with 0.5 mg. of progesterone. These experiments are subject to the difficulty that they involve varying the dosage of two hormones simultaneously. The animals used by Hisaw and Greep were, moreover, relatively young, and the progestational changes involved were not as elaborate as the natural progestational state. The result fits however those obtained above in giving 150 international units of estrone as somewhat less than an
{ 191 }
THE HORMONES IN HUMAN REPRODUCTION
adequate substitute for what the animal's own ovaries produce.
Probable daily output of estrogenic hormone by the monkey. By all these means of estimation we arrive at the result that the probable daily output of estrogenic hormone by the young adult Rhesus monkey is equivalent to somewhat more than 150 international units and may be set tentatively at the equivalent of 200 international units of estrone. This is a minimum figure; the true amount may be greater, but can hardly be smaller.
This estimate is based necessarily on the assumption that an ovarian hormone injected once daily in oil solution is utilized by the body as efficiently as hormone produced in the animal's own ovaries. There is at present no way of ascertaining how nearly this is true, but in any case, the slow absorption of an oily solution must afford a fairly good imitation of natural processes, and we may recall that my estimate of the rate of secretion of progesterone, which involved the same assumption, turned out to be near the truth, when checked by the recovery of the excretion product, pregnanediol.
Administration of estrogenic hormone in pellets. In recent years many experimental workers have been administering estrogenic hormones by compressing them into small hard pellets which are buried under the skin. This method has the advantage that the hormone is absorbed continuously from the surface of the pellet, whereas when given by injection the rate of absorption fluctuates, being high just after an injection and lower as more and more of the injected dose is absorbed. For this reason a given effect is obtained from a smaller daily dose when absorbed from a pellet than when injected. Pellets will probably be used in human cases in which long continued action is required, not only because of the continuous absorption, but also because insertion of the pellet, which can be done through a hollow needle, avoids repeated hypodermic punctures.
{ 192 }
ENDOCRINE ARITHMETIC
It becomes important for our present calculations to kjiow just how much more effective this method is, dose for dose, than injections, because our estimate of the daily need for estrogenic hormone is based on comparison with injected doses. At first sight the results obtained by pellets seem to be achieved by very small doses indeed, and it is generally taken for granted that the method is much more effective than injection. Very little, however, is known about the exact comparison by actual experiment. Carl G. Hartman has reported, for instance, that the sex skin of a Rhesus monkey was kept red and swollen for 4 months with a single 3-milligram pellet of estrone. This seems small, but assuming that the pellet was entirely used up, this gives a daily dose of 0.025 mg. or 250 international units (3 mg. divided by 120 days). Hartman's monkey thus actually received a larger daily dose than is called for on the basis of our estimate, namely 200 international units.
Deanesly and Parkes of London, who introduced the pellet method, cite an experiment with one of the male hormones which indicates that the dose by pellet is about one-half that by injection. I have heard of experiments with another male hormone in which the ratio was 2 to 3. If any such proportion as these is true of estrone, then our calculated daily output of estrogen by the monkey is roughly one-third to one-half too large.
But here again we are guessing. What evidence is there that absorption from a pellet is really comparable to the natural absorption of the animal's own hormone from the ovarian cells? Nobody knows the answer to this. It might even be true that the pellets yield their substance to the blood stream more easily than do the cells of endocrine glands, in which the hormone is made and stored within the cellular substance. The big molecules of the hormone have to make their way through the outer layers of the cell, not merely drop off the surface of a pellet.
{ 193 )
THE HORMONES IN HUMAN REPRODUCTION
In short, it would be premature to let the pellet method outweigh, in these very crude calculations, the results from injections, about which at present wc know very much more; and therefore I propose to maintain for the present the estimate arrived at above, namely that a female Rhesus monkey produces from her two ovaries estrogenic hormone equivalent to about 200 international units of estrone daily.
If this were actually estrone, the daily output would weigh 0.02 milligram.
Application of these calculations to the human female. Can we apply this estimate to the human female? A woman weighs on the average 15 times as much as a monkey. Two hundred international units x 15 gives 3,000 international units as the daily output of the woman's ovaries. Various medical observations which have been published might be analyzed to give us some sort of check on the estimate. My friend, W. M. Allen, for example, informs me that in his treatment of women whose ovaries had been removed previously he could induce menstruation-like bleeding with estrogenic hormone equivalent to about 4,200 international units of estrone daily. This figure, which is the most pertinent I can find, is roughly 50 per cent higher than my calculation from the monkey experiments, but we have no way of telling how closely this amount compares with that needed by a normal woman. Perhaps what Allen was trying to do required more, perhaps less, than the normal output.
Unfortunately we cannot get help in this problem by measuring the estrogen discharged in the urine, because we do not know just what relationship exists between the hormone which is at work in the body and that which is excreted. The number of milligrams of estriol and similar substances recovered from the urine does not tell us how much of the ovarian hormone was made and used in the body (Appendix II, note 16).
This chapter has contained, after all, a good deal of valiant
{ 194 }
ENDOCRINE ARITHMETIC
shooting in the dark. Our conclusions and estimates are sure to be better in time to come. Meanwhile the reader will perceive that after the excitement and drama of the pioneer phase of research on the ovarian hormones, we are in for a lot of tedious, unspectacular measurement and computation, until the reactions of these substances in the body are quantitatively known as well as the chemist knows the reactions in his flasks. Then, as Lord Kelvin said, we shall really understand our subject.
{ 196 }
THE HORMONES IN PREGNANCY
Long was I hugg'd close — long and long.
Immense have been the preparations for me. Faithful and friendly the arms that have help'd me. Cycles ferried my cradle, rowing and rowing like friendly
boatmen. For room to me stars kept aside in their own rings. They sent influences to look after what was to hold me. Before I was born out of my mother generations guided me. My embryo has never been torpid, nothing could overlay it.' — ^Walt Whitman, Song of Myself.
CHAPTER VIII THE HORMONES IN PREGNANCY
THE maintenance of pregnancy is a truly complex afFair. A living creature is growing at a tremendous rate inside a hollow chamber, the uterus. This organ must at first tolerate, even support the newcomer. It must grow in size and strength so that its enterprising tenant may not overwhelm it (Fig. 28). All the other muscle-walled organs of the body are built to keep things moving — the heart, the intestines, the bladder for example — and so, ultimately, is the uterus. For nine months, however, it must be kept in check and not allowed to expel the infant prematurely. Then all of a sudden its energies are released and it is called upon to deliver its contents into the world, through the narrow bony canal of the pelvis, with sufficient force and speed on one hand, and sufficient gentleness on the other, to avoid wearing out the mother or crushing the baby. To use a current expression of bewilderment, figure out all that if you can ! Nature, indeed, has figured it out reasonably well ; but when the physiologist attempts to discern the factors of this multifarious process and to see how they are set in motion, timed, and controlled, he finds he has yet a long research ahead of him.
In this book we can do no more than sketch the problems involved. In outline, what has to be worked out is the growth and function of a muscular organ, controlled in part by the nervous system, in part by hormones. The latter are those which come from the ovary, the pituitary and the adrenal, together with the output of a new source, peculiar to pregnancy, the placenta.
THE PLACENTA
Once the embryo is safely lodged in the uterus and has begun to grow, a new era of hormone activity begins. The
{ 199 }
THE HORMONES IN HUMAN REPRODUCTION
Fig. 28. Enlargement of the human uterus during pregnancy. At v, virginal uterus; the large hatched area is the pregnant uterus, at full term, drawn to same scale, approximately % natural size. Adapted from a figure by Stieve.
task of the ovary is not yet over, but its functions are in large part to be taken up, reinforced, and even superseded by a new organ of internal secretion, the placenta. The human placenta is an object of considerable size, as shown in the fine old engraving from Casserius (Plate XX). When fully developed it is about 18 centimeters (7.5 inches) in diameter, and weighs 500 grams (a little more than one pound) on the average. When in place in the uterus, its structure is like nothing else so much as the matted roots of a tree planted in a tub. The roots simulate the villi of the placenta, which carry within their slender strands the finest branches of the blood vessels coming from the infant in the umbilical cord. Through these delicate vessels the blood of the infant circulates in a constant and rapid stream. The tub in which we imagine the tree planted simulates the pool which the embryo has excavated for itself in the wall of the mother's uterus (Fig. 14, p. 58).
{ 200 }
THE HORMONES IN PREGNANCY
Through this pool the mother's blood slowly flows, out from the arteries that supply the region and back into the veins, bathing the rootlike villi of the placenta. From the mother's blood to the blood of the embryo, oxygen and dissolved foodstuffs filter through the covering cells of the villi and through the thin walls of the blood vessels that run along within them, just as nutritive substances pass into the roots of a plant from the moist soil in which they grow. The infant sends back carbon dioxide, urea, and other wastes from its tissues, to be filtered out through the placental vessels into the mother's blood, which carries away these wastes to be disposed of with the products of her own metabolism.
The covering cells of the villi are called upon, however, not only to take part in the process of filtering foodstuffs inward and waste products out, but also to produce a whole series of endocrine substances. This important fact is unfortunately masked by a great deal of confusion in our present knowledge. The placenta differs greatly in different species, not only in its structure but also in its endocrine activities. Statements which are true of one species may not apply at all in others. For this reason our discussion will be limited to the human species (except as specifically stated) and even then we shall be restrained by a certain amount of uncertainty. To begin with, the placenta begins very early in pregnancy to elaborate a hormone of its own, having profound gonadotrophic properties (that is, power to stimulate activity of the ovary and the testes) much like that of the pituitary gonadotrophic hormones.^ This activity begins, indeed, before we can properly speak of the placenta, for the hormone in question is made by the cells (i.e. the trophoblast) covering the early villous processes that surround the embryo, as soon as they
1 For the sake of clearness, it seems best to refer to the gonadotrophic material in the singular, i.e. "a hormone," but actually it seems to be a hormone complex comprising two substances, one of which tends to stimulate growth of the follicles, the other to convert the follicles into corpora lutea (Appendix II, note 11).
{ 201 }
THE HORMONES IN HUMAN REPRODUCTION
begin to grow. Knowledge of this subject goes back to 1928, when Aschheim and Zondek, then of Berlin, found that during pregnancy the human urine contains something that has a powerfully stimulating effect on the ovaries of young mice and rats. This provided the basis for the now famous AschheimZondek test for pregnancy. The urine of a pregnant woman, injected into an infantile mouse or rat, produces prompt and characteristic signs of activity in the ovarian follicles. An even quicker test for pregnancy is provided by a modification of this procedure, introduced by Maurice Friedman, an American investigator. In the Friedman test the urine, either raw or partially purified by precipitation with alcohol, is injected into the ear vein of a rabbit. If the patient is pregnant, the rabbit ovulates about 10 hours after the injection. This hormone test for pregnancy is (in both variations) probably more nearly infallible than any other biological test used by physicians, for when properly performed it is accurate in better than 98 per cent of all cases.
The gonadotrophic hormone complex of the urine can also be extracted from the placenta and in all probability is made there. George O. Gey, a tissue culture expert of Baltimore, recently showed that placental tissue growing in his test tubes | was able to produce a gonadotrophic substance. Chemically the urinary gonadotrophic material is protein, like the gonadotrophic hormone that is produced in the pituitary gland, and indeed it is so much like the latter that it was for a time considered to be identical with it, but clear differences between the two substances have been observed, as evidenced by the details of their effects on animals of various species. The placental gonadotrophic hormone complex appears in the urine in the first month of pregnancy, in sufficient amount to give a positive Aschheim-Zondek or Friedman test. It is present throughout pregnancy, but reaches its greatest amount in the second month and falls off rapidly thereafter. In the Rhesus monkey it is found only between the 18th and the 25 th day. In
{ 202 )
THE HORMONES IN PREGNANCY
the blood of the pregnant mare there is a gonadotrophic hormone which also has a stimulating effect on the ovaries of test animals, such as rats, differing considerably, however, in detail. This does not get into the urine in significant amounts, which means that it must be different chemically from the human hormone of similar action.
We do not know why these substances can be found in some species of animals and not in others, nor do we know what function they perform in pregnancy. The whole series of pituitary and pituitary-like hormones has been extremely difficult to investigate chemically because the substances are proteins and they defy purification. The ovaries of the rat and the rabbit can distinguish them better than the chemist. For the present we must content ourselves with being grateful for the pregnancy test and await the day when these troublesome substances yield themselves to chemical isolation.
As mentioned previously (Chapter IV) the urine of pregnant women contains relatively large amounts of estrogenic substances, which increase as pregnancy advances and disappear after parturition. These substances have been found in the urine of several other species during pregnancy. The human placenta also contains large amounts of estrogenic hormones, chiefly estriol, and is almost certainly the source of those which appear in the urine. As mentioned in Chapter IV, when the ovaries are removed during pregnancy, estrogens continue to be excreted in the urine, a fact which proves that some other source exists, and this can hardly be anything else than the placenta. A similar situation, produced experimentally in the monkey, has been studied very carefully and reported by R. L. Dorfman and Gertrude Van Wagenen of Yale Medical School.
There are several possible ways in which the production of estrogens by the placenta may be useful. It has been suggested that these hormones are needed, in larger amounts than the ovaries can provide (a) to promote the growth of the uterus
{ 203 }
THE HORMONES IN HUMAN REPRODUCTION
which occurs during pregnancy; (b) to cause growth of the mammary glands to get them ready for the production of milk; (c) to set up contractions of the uterus when the time comes for parturition ; (d) to cause persistence of the corpus luteum. These possibilities will be discussed again later in this chapter.
As regards progesterone in the placenta, it has already been pointed out that in some animals the corpora lutea are indispensable until the end of pregnancy. In the rat and the cow, for example, the ovaries cannot be removed at any time without causing loss of the embryos, and the corpora lutea appear to be functional until almost the end of gestation. In the human species, on the other hand, the ovaries can be removed without affecting the survival and birth of the infant, as early as the third month of pregnancy. After such an operation pregnanediol has been found in the urine, an indication that progesterone has continued to be produced somewhere. Naturally the placenta has been suspected, and assays have yielded small amounts of progesterone or a substance of closely similar kind.
ACTION OF THE HORMONES IN PREGNANCY
We can do hardly more here than sketch what is known about the multifarious interactions of the hormones in pregnancy. Readers who wish to follow the subject in detail may consult the excellent book on this subject by my colleague S. R. M. Reynolds.^ In the first place, the two ovarian hormones contribute to the growth of the uterus. Growth of the muscular wall is known to involve (as one might well expect) first an increase of the number of the muscle cells, and then an increase of the size of the individual cells. In the human uterus the measurements of the German histologist Stieve indicate that the muscle cells are 17 to 40 times larger at the end of
2 Physiology of the Uterus, with Clinical Correlations, by Samuel R. M. Reynolds, New York, 1939.
{ 204. }
THE HORMONES IN PREGNANCY
pregnancy than in the empty uterus. Other elements of the uterine wall, namely the connective tissue, blood vessels, and nerves, also increase in amount. In this process the estrogenic hormone contributes its general growth-promoting effect, which it exerts by augmenting the blood flow through the tissues of the uterus. Under its influence there is some increase in number of the uterine cells. Progesterone in turn causes a decided wave of cell division in the muscle, and then within a few days at the beginning of pregnancy there is a large increase in the number of muscle cells. Subsequent growth of the individual cells, and consequently of the whole wall of the uterus, comes about as the result of stretching by the growing embryo. As the uterus is distended it grows in thickness and strength; if this were not so, the infant would soon rupture the walls that confine it. Everyone is, of course, familiar with the fact that working a muscle makes it grow, and this is no less true of the involuntary muscles of the internal organs than of the skeletal muscle; but like most other familiar responses of the body, we often take it for granted without realizing how little we know how it comes about. Why the uterine muscle grows when that organ is distended is a large question of general physiology, beyond the scope of this book. Reynolds has shown that if he distends the rabbit's uterus by introducing pellets of wax, it will grow in thickness just as it does in pregnancy. By this means he has been able to test the eff*ects of the ovarian hormones upon the growth-response to distention, and has found (among many other interesting facts) that treatment with estrogenic hormone cuts down this response. This hormone, then, which at first helps start the growth of the pregnant uterus, afterward helps to control it. In human pregnancy we know there is plenty of estrogen available in the later months; in all probability this serves to keep the growth of the uterus from going too far. With this hint that the interplay of the hormones is indeed complex,
{ 205 }
THE HORMONES IN HUMAN REPRODUCTION
we had better leave the subject to the specialists for further study.
Finally the time comes when gestation can go on no longer. The uterus, overburdened by its rapidly growing tenant, must deliver itself. Degenerative changes begin in the placenta, the nourishment of the infant is thereby impaired, and the uterus commences its efforts to expel the child. This it accomplishes by means of strong contractions, efficiently timed and coordinated so that the infant is pushed toward the outlet of the uterus. The uterine orifice, and afterward the vaginal canal, are stretched open to allow passage of the infant, while the rest of the uterus contracts to provide the necessary force. There is no simple explanation of the onset of labor. Many physicians and biologists have tried to discover some simple reason why at a particular time — 9 months in the human, 2 years in the elephant, 21 days in the mouse, or whenever, according to the species, the fated hour arrives — the act of parturition begins. It has been thought, for example, that the uterus is at last simply stretched too far and is thereby irritated into contracting again; or that the breakdown of the placenta constitutes a stimulus to the uterine muscle ; or that some chemical substance from elsewhere in the body sets the muscle into action. When it was discovered that estrogenic hormones stimulate the involuntary muscle of the uterus, and that progesterone tends to relax it, an attractive theory of the cause of labor at once suggested itself. We need only suppose that when the end of gestation draws near, the production of progesterone goes down, and estrogenic hormone is thereby allowed to build up contractions of the uterine muscle. This hypothesis is however much too simple, as Reynolds points out in the book cited above. For one thing, the contractions of the uterus in labor are very different in their timing and coordination from those of the nonpregnant uterus. The fact is that the uterus at the end of pregnancy is operated by a very elaborately organized set of adjustments.
{ 206 }
THE HORMONES IN PREGNANCY
The proportion of the infant to the space it occupies; the strength of the uterine wall and the pressure it exerts upon its contents; the rate of blood flow through the uterus; the sensitivity of its muscle and nerves ; the balance of the hormones that affect it; the nutrition of the infant and the placenta — all these factors (and others beside them, for all we know) are balanced one against the other and when the crisis comes they are all involved at once. The physiologist who looks for one specific cause of the onset of labor is up against the same kind of problem as the economist who tries to find one single cause for a stock market crash or to pin down a nationwide problem of unemployment to one specific factor. When dealing with such complex affairs as those of a nation or a pregnancy the investigator cannot isolate one factor at a time and study it singly. He has to unravel a whole system of balanced forces. In the problem we are considering, the hormones are certainly to be numbered among the most important factors, but it is scarcely safe at present to say more,
LACTATION
When the mother's body has completed its provision of shelter and nourishment for the child by means of the hormones and has seen him safely into the world, it has yet another service to render on his behalf — namely that the breast for which he will so promptly cry is ready to supply him with milk.
The recent discovery of a specific hormone for lactation, in the pituitary gland, was a great surprise. It involved a simple little piece of scientific logic which the reader may enjoy after the preceding complexities of this chapter. We had better clear the way for this story, however, by recalling to mind the earlier history of the mammary gland. When a girl or a young animal reaches sexual maturity, the mammary glands are brought from the immature state to the adult con { 207 }
THE HORMONES IN HUMAN REPRODUCTION
dition, by action of the estrogenic hormone. Nothing is more striking than to watch the growth of the mammary glands in a young animal receiving estrogen. Each gland is a system of branching channels lined by cells derived from the outer layer of the skin (epidermis). Long before birth these ducts begin to grow from the nipples and to spread out around them in a little circle under the skin. At first the channels are few and short, and only slightly branched (Fig. 29, A). Under the action of the estrogenic hormone they branch extensively and spread to adult dimensions (as indicated in the diagram, Fig. 29, B). In the girl at puberty this is, of course, a gradual change, but in an experimental animal under hormone treatment it can be produced quite rapidly. The nipples quadruple in size in a few days, and the ducts push outward in a widening circle. In pregnancy a much greater development occurs. The branches of the duct system develop extensive terminal twigs ending in secretory alveoli (Fig. 29, C, B). These become more numerous as pregnancy advances. Finally, globules of milk-fat accumulate in the cells of the alveoli (Fig. 29, E). The actual flow of milk in quantity does not begin, however, until after parturition.
From the time it was first conjectured that the corpus luteum is a gland of internal secretion, until quite recently, it was supposed that this particular endocrine organ is responsible for the growth of the mammary gland in pregnancy and the secretion of milk. On the face of it, there could hardly be a more plausible conjecture, for the growth of the mammary gland closely follows the appearance of the corpus luteum, and is so obviously a part of the general preparation for the infant that it seems very logically to go with the other functions that the ovary exerts during pregnancy.
If this is true, however, why does not the corpus luteum produce mammary growth and even lactation not only in pregnancy but in each ovarian cycle.? To this query A. S. Parkes of London in 1929 offered the tentative reply that
{ ^08 )
THE HORMONES IN PREGNANCY
Fig. 29. Diagrams illustrating the development of the mammary gland as seen in laboratory animals. A, mammary gland of immature animal, consisting of simple ducts radiating from the nipple. B, small area of A enlarged to show adult virginal gland. The action of estrogenic hormone has produced extensive growth and branching of the ducts. C, small part of B enlarged again to show the effect of pregnancy; there has been a great development of duct twigs with terminal alveoli. D, terminal alveoli enlarged to show their cell-structure. E, secretion of milk globules by the cells of the alveoli. Based on a figure by C. W. Turner In Sex and Internal Secretions.
perhaps in the ordinary cycle, in which the corpus luteum lasts but two weeks, there is not time to build up the mammary gland sufficiently. He therefore ingeniously proposed to apply the discovery, then quite new, that the corpora lutea can be made to persist for weeks by injection of anterior pituitary extract. He tried this experiment in rabbits, by mating them to males rendered infertile by having their seminal ducts
{ 209 }
THE HORMONES IN HUMAN REPRODUCTION
blocked, so that these females ovulated but did not become pregnant. The corpora lutea, which under these circumstances would normally degenerate after about 14 days, were made to persist by the pituitary hormones. The expectations of the experimenter were brilliantly fulfilled by the occurrence of mammary growth and lactation. When the report of these experiments reached the United States, we had in our University of Rochester laboratory a fair amount of the then new corpus luteum hormone in crude form (progestin) and took the obvious step of trying to produce mammary growth and lactation with the progestin alone. To my surprise we got no lactation and no marked growth of the mammary gland. From this failure, however, an important deduction could be made. Parkes had subjected his rabbits to the action of two hormones (pituitary and corpus luteum) ; I had given only the latter. He obtained lactation, I did not. Subtracting my procedure from his, it looked as if the anterior pituitary hormone was the only necessary factor. We made up a flask of pituitary extract from sheep and injected it into six adult castrated virgin female rabbits. In 3 days milk began to drip from their nipples ; in 10 days the mammary glands had thickened and spread all over the chest and belly as in advanced pregnancy and when we milked them the milk spurted across the room.
I thought at first that this discovery of the lactogenic potency of the anterior lobe of the pituitary was completely new, but study of the scientific journals revealed that a few months previously two Alsatians, Strieker and Grueter, working in Strasbourg in the laboratory of Paul Bouin, had done exactly the same experiment with the same result. By what process of logic they were led to try it was not narrated in their report.
The extracts were very crude and we set out to purify them. One of the large drug houses provided more extract by the quart and one of their research staff started to work out
i 210 }
THE HORMONES IN PREGNANCY
the chemical separations, but be and I found only that we were dealing with a protein, after which we simply got lost in this most difficult field of biological chemistry. Meanwhile my genial and versatile friend Oscar Riddle of the Carnegie Institution (Department of Genetics, at Cold Spring Harbor), ably assisted by his colleague R. W. Bates, applied his allround knowledge of tissue chemistry to the task and succeeded in purifying the hormone to a considerable degree. He called it prolactin. The complete chemical isolation and chemical identification of this important substance is now a problem for the most advanced special experts in the chemistry of proteins (Appendix H, note 17).
There is a queer sequel of this discovery of prolactin, which opens a vista of the long past origin of the hormones in evolutionary history. This story has to do with pigeons' milk. Not that pigeons have mammary glands ; but females of the genus actually secrete into their crops a kind of milky secretion which they regurgitate and feed to their nestlings. This crop-milk is produced by special glands in the lining of the crop. Dr. Riddle knows all about pigeons ; he has been studying their physiology for years and had a fine collection of them at Cold Spring Harbor. Impressed by the parallelism between the formation of crop-milk and mammalian lactation, he administered his extract of beef pituitaries to some of his female pigeons and got proliferation of the crop glands just as if they were mammary glands. This reaction is so easy to produce that it is now the standard test for prolactin. The strangest part is, however, yet to be told. The eggs of the amphibians (frogs, toads, and salamanders for example) are laid in the water and the embryos have the benefit neither of nest and crop-milk nor of uterus and mammary gland. When the eggs are shed by the mother, however, they are protected by an envelope of jelly, laid on in the mother's oviduct. An Argentine physician, already mentioned in this work. Dr. In^s de Allende of Cordoba, has discovered that a hormone
{ sii }
THE HORMONES IN HUMAN REPRODUCTION
like that found in extracts of beef pituitary glands is responsible for the secretion of the protective jelly of the eggs of toads. She elicited this function by inserting pieces of toad or beef pituitary gland under the skin of her toads, thus increasing the available amount of pituitary hormones; and in a few cases she could even elicit it by injecting Riddle's prolactin.
Here, then, are three particular means of provision for the newborn infant, occurring in three widely different branches of the animal kingdom, and adapted to offspring living under very dissimilar circumstances, yet all these secretions are controlled by the pituitary gland and can be induced by extracts of beef pituitaries. The embryologist perceives a further remarkable feature of this story. The mammary gland, he knows, is derived from the outer of the three fundamental tissue layers of the embryo, the ectoderm'^ the crop glands of the pigeon are derived from the inner layer, the endoderm ; and the secretory lining of the toad's oviduct is derived from the middle layer, the mesoderm. These three tissues from which the pituitary gland elicits reactions of such similar usefulness, are about as widely different in their position in the body, and in their embryological history, as they can possibly be, but when in the evolution of toad, bird, and mammal there was need to call upon them to foster the fledglings of their kind, the pituitary gland took control in each case.
Has the corpus luteum, then, no role whatever in the processes leading to lactation, and can the pituitary extracts induce lactation in a mammary gland prepared only by estrogenic hormone.'* My rabbits seemed to indicate that this is true, but Strieker and Grueter declared that their pituitary extracts were not successful unless there had been corpora lutea in the ovaries at some time during recent months ; in other words, the pituitary lactogenic hormone appeared able only to jact upon a mammary gland sensitized by progesterone. This difference in the findings led to a great deal of
{ 212 }
THE HORMONES IN PREGNANCY
subsequent work by various investigators, well summarized by C. W. Turner of Missouri, himself one of the leaders in this work, in Sex and Internal Secretions} It now appears that the second of the three more or less distinct stages of growth and function of the mammary gland, already referred to and illustrated (Fig. 29), involves somewhat different responses to the hormones in different species. The first stage, that of preliminary growth of the duct system to the adult virginal state, occurs under the influence of estrogenic hormone as already described. In the second stage, the ends of the ducts proliferate and branch into numerous terminal alveoli. This stage in many animals requires the action of progesterone ; in a few species (of which the guinea pig is an example) progesterone is not needed at all and the proliferation can be completely induced by the estrogens ; in some other species growth of the alveoli is at least facilitated or speeded up by progesterone, though not actually dependent upon that hormone. Judging from various observations which have been reported on monkeys, the primate mammary gland is among this intermediate group. Whether this is also true of the human we do not know at present. The third stage, that of secretion of milk, is brought about by the lactogenic hormone of the pituitary. It is a striking evidence of the potency of these hormones to induce lactation that the rudimentary mammary glands of male animals can readily be made to lactate by a suitable course of treatment with the estrogenprolactin or estrin-progesterone-prolactin sequence.
We have yet to discover how the pituitary gland is stimulated to exert its lactogenic effect during pregnancy. The reason the flow of milk does not begin until just after parturition, and then begins suddenly, is that lactation is inhibited by the estrogenic hormone of the placenta. Once the placenta is out of the way, the flow of milk is released.
8 Sex and Internal Secretions, edited by Edgar Allen, Baltimore, 2d ed., 1939; Chapter XI, The Mammary Glands, by C. W. Turner.
{ 213 }
THE HORMONES IN HUMAN REPRODUCTION
The induction of lactation in pregnancy is thus another example of those remarkable integrative linkages among the various parts of the reproductive system by means of hormones, by which shelter, warmth, and nourishment are provided for the mammalian egg while it is incubated within the body and at the breast of its mother. By such extraordinary means as this have the children of men, latest of a long series of creatures to haunt the earth, been protected from isolation and danger in their earliest days, and given time to grow for nine months before being exposed to the rigors of the outer world. This privilege of uterogestation, which would be impossible without the ovarian and placental hormones, gives an incalculable advantage to mankind and the other mammals in the struggle for superiority in the animal kingdom.
i
{ IBU)
THE MALE HORMONE
'She \^Nature'\ spawneth men as mallows fresh, Hero and maiden, flesh of her flesh; She drugs her water and her wheat With the flavors she finds meet. And gives them what to drink and eat; And having thus their bread and growth. They do her bidding, nothing loath."
— Ralph Waldo Emerson, Nature II.
CHAPTER IX
THE MALE HORMONE
THE male sex glands (testes) of man and the other mammals, like the ovaries, perform a double task. They exist primarily, of course, to produce the male germ cells. In primitive aquatic animals this is all they need to do. The Hydra, for example, shown in Plate II, C, in the act of discharging its sperm cells directly into the v/ater, has fulfilled its reproductive task for the season, and its empty testes are of no more consequence than a spent skyrocket. In mammals, however, things are not so simple. There are other needs that can be fulfilled only by the coordination of various parts of the body by means of a hormone. Not only must the sperm cells be formed and ripened ; they must also be stored until they are needed in mating. What is more, they must be stored in a most particular way, immersed in a watery environment, for the mammals have never fully shaken off their ancient adaptation to the sea. They spend their lives on land, but when the time comes to reproduce their kind, their spawning requires salt water — not indeed the actual sea, but the internal fluids of the generative organs. The egg ripens in the fluid of the Graafian follicle. The sperm cells accomplish their tortuous journey to the Qgg by swimming, and the offspring of all the mammals spend the long term of gestation in a submarine environment. You and I cannot remember our ancestral life in the water, nor the nine months we ourselves lived beneath the chorio-amniotic sea, but our tissues recall it ; the skin, the kidneys and the adrenal glands working to hold sufficient water and just enough salt, the testes providing through their accessory organs those fluids in which the sperm cells may be effectually launched upon the sea of life.
In another way also the endocrine function of the testis becomes necessary. The higher animals lead complicated lives.
{ 217 }
THE HORMONES IN HUMAN REPRODUCTION
They wage a varied battle for existence and are swayed by many circumstances. Perpetuation of the race amid such distractions requires especially active maintenance of sexual vigor and the urge to mate. This too becomes a function of the testis as an organ of generation.
THE MALE REPRODUCTIVE ORGANS
The testis. To follow the story in detail we must first review the anatomy of the testis and the associated male organs of reproduction. The diagram (Fig. 30) will serve to orient us. The two testes lie in their pouch of skin (scrotum) . They are objects of ovoid shape, about the size of walnuts, that is to say 4.5 x 3 centimeters (2x1% inches) in diameter. Within these small rounded bodies the business of sperm cell production is carried on inside an extraordinary system of tubular canals. The testis, in fact, consists essentially of many hundred small tubules, called seminiferous tubules, each about 30 to 70 centimeters (1 to 2 feet) in length and about as large in diameter as a strand of sewing silk. These tubules are coiled very tightly in the small space available, and thus when we look through the microscope at a section of the testis, we see countless sections of the individual tubules, cut in every possible direction (Plate XXIII, A). How they actually run, and how they are connected, was for a long time one of the most difficult problems of microscopic anatomy. We should get a similar picture if we took a thoroughly tangled ball of twine and cut a section through it with a sharp knife. Nobody could possibly tell from such a cut whether the ball of twine contained one long piece of twine, or several shorter ones, or how they were joined together. Likewise a section of the testis cannot tell us anything about the course of the seminiferous tubules. For a century microscopists applied their various technical tricks to this problem, including the making of magnified models from serial sections, but with only imperfect success, owing to the difficulty and laboriousness of following
{ 218 }
1.#
^.•v:^v^£^:-^'*3^
Plate XXIII. ^, portion of human testis and epididymis, magnified 10 times. The large circles and loops at the right are sections of the coiled tube of the epididymis; the smaller tubules filling the left two-thirds of the picture are the seminiferous tubules of the testis. B, area of the same testis magnified 200 times, showing 5 clumps of interstitial cells between the tubules. Photographs from preparation lent by Joseph Gillman through I. Gersh.
■V t-i .IS' ©■_•■"!¥ -r -Jin,'
t
\
'^â– ^.,>
^^ 4, V-' ..-:> ^^^^ '^ "^ #
Plate XXIV. A, portion of seminiferous tubule of rat, showing formation sperm cells. Note the peculiar hook- or halberd-shaped heads and long tails of tl rat's sperm cells (form of human sperm cells shown in Fig. 7). Magnified 600 time From specimen lent by K. E. Mason. B, portion of seminifierous tubule of unde scended (cryptorchid) testis of pig. Note that sperm cell formation is totally absent, the tubule being lined by ill-defined cells (epithelial cells). The interstitij cells are, however, well preserved. Magnified about 600 times.
THE MALE HORMONE
these minute and lengthy canals. Finally in 1913 the problem was cleverly solved by the late Professor Carl Huber of the University of Michigan, who worked out a method of soften
Fio. 30. The human male reproductive system. From Attaining Manhood, by George W. Corner, by courtesy of Harper and Brothers.
{ 219 }
THE HORMONES IN HUMAN REPRODUCTION
ing the testis with acid and then, with incredible patience and dexterity, dissected out complete tubules under the microscope with fine needles and mounted them, without breakage, on glass slides. He found that they are arranged in loops or arches, all opening into a network of channels at the hilum a of the testis, whence they are drained off by a dozen larger | channels into the epididymis. All these facts have been depicted in Fig. 31.
In cross section under high magnification (Plate XXIV, A ) the tubules are seen to be lined by several layers of cells. The outermost layer (i.e. that farthest from the central channel of the tubule) is made up of large clear cells. As these divide to form the next and succeeding layers, the cells become smaller. Finally little is left except the nucleus, and even this becomes more compact. A long tail-like process grows out of the rapidly shrinking cell. This figure represents the rat's sperm cells with their hook or halberd-shaped heads. The completed human sperm cell is shown in Fig. 7. It has a total length, including the tail, of about 60 microns or 1/400 inch. The head is about 5 microns long by 3 wide. The sperm cell is therefore by far the smallest cell in the body. An idea of its relative dimensions may be gained by comparing it with the printed period at the end of this sentence. If the sperm heads were laid like a pavement, one layer deep, on such a dot, it would take about 2,500 of them to cover it. About 12 eg^ cells could be placed on such an area.
As the sperm cells are formed, little clumps of them cling to supporting cells in the lining of the tubules until finally they drop off and are carried along the channel toward the seminal ducts. In animals that breed at all seasons of the year, for instance man, rat, rabbit and guinea pig, sperm production goes on continuously, passing in waves along the tubules, so that sperm cells are always available. Many wild species, however, have distinct breeding seasons once a year, and in these there is a cycle of testicular activity. In the seasons of inactivity spermatogenesis ceases and the testis diminishes in size.
Fig. 31. Arrangement of the tubules of the testis, the epididymis, and the seminal duct. Adapted from Spalteholz and Huber. From Attaining Manhood, by George W. Corner, by courtesy of Harper anl Brothers.
The testis, like the ovary, is under control of the pituitary gonadotrophic hormones. One of the most striking results of the brilliant campaign of investigation of the pituitary led by Philip E. Smith, now of Columbia University, has been the discovery (1927) that removal of the pituitary gland from an adult male causes degeneration of the testis, and in an immature male prevents the development of sperm cell formation. The implantation of bits of pituitary gland or the injection of pituitary extracts will substitute for the missing organ and prevent degeneration of the testis. In some species, but not in others, success has been attained in starting sperm formation in immature animals by injecting pituitary extracts.
Another remarkable discovery about spermatogenesis was announced by Carl R. Moore (University of Chicago) in 1924, namely, that the mammalian testis cannot form sperm cells unless it is subjected to a temperature slightly lower than that of the interior of the body.^ In its normal place in the scrotal sac the testis is under temperature conditions exactly suited to its function. It has long been known that a man with undescended testicles is not fertile, and horse breeders are well aware that the same is true of cryptorchid stallions. They often call upon veterinary surgeons to bring down the testes of colts by operation. Moore's investigations have given us the reason for this sterility. In man descent of the testes normally occurs before birth. The sex glands are formed in the abdominal cavity near the lower pole of the kidneys, but they gradually move downward (or as some embryologists prefer to say, the body grows upward past the testes) until they have fully descended and have occupied their permanent place in the scrotum. Just why this elaborate transfer of the testes takes place, seemingly leaving them less protected than if they remained in the abdominal cavity, as in lower vertebrate animals, has never been satisfactorily explained. One can only guess that when the process of evolution of the warm-blooded condition was accomplished, Nature discovered (so to speak) that after all the testes could not stand the temperature at which she had stabilized the mammals, and had to get them to a cooler place; but any such conjecture seems to put Nature (or whatever you choose to call the forces that guide evolution) in a position like that of tariff legislators, chess players and others who find that one change in a complicated situation may set off unexpected changes elsewhere. At any rate, descent of the testes is a deep-seated phenomenon that has become essential to fertility. The inside of the scrotum is several degrees cooler than the abdominal cavity, because the scrotal sac has thin walls and no insulating layer of subcutaneous fat, but numerous sweat glands by which it loses heat. Moore found that if he put the testis of a guinea pig or other animal back in the abdominal cavity (preserving its blood supply) and stitched it there, the seminiferous tubules became disorganized within a week, but recovered if he brought them down again before the damage had become permanent. He took also a fertile ram and wrapped its scrotum in woolen coverings so that the testes were brought to the temperature of the rest of the body. This too caused cessation of sperm production. Actual direct heating of the testis has a similar effect. A single exposure of the guinea pig's testis for 15 minutes to a temperature 6 degrees above that of the interior of the body causes degeneration of the seminiferous tubules. It is known that in man high fevers are followed by temporary loss of spermatozoa.
1 For a full account of this subject, see Sex and Internal Secretions, edited by Edgar Allen, 2d ed., Baltimore, 1939; Chapter VII, "Biology of the Testes," by Carl R. Moore.
Descent of the testis into the scrotum is part of the general pattern of the development of the sex gland and is therefore subject to control by the pituitary and pituitarylike hormones. It has been known for about 10 years that gonadotropic hormones from pregnancy urine can be used for the treatment of non-descent of the testis in boys. It does not always succeed, for adhesions and other obstacles may interfere; therefore the treatment must be used only in selected cases after thorough study. When the hormone fails, surgical methods are usually still available.
Interstitial cells. In the angular spaces between the tubules the microscope reveals little clumps of relatively large cells not in any way connected with the sperm-forming cells (Plate XXIII, B), Although there are only a few cells at any one point, there are so many clumps that the total mass of the interstitial cells adds up to a significant proportion of the whole testis. Some writers call the totality of these cells "the interstitial gland." There is an ample network of capillary blood vessels among these cell clumps. The arrangement is obviously like that seen in the glands of internal secretion; and it is in fact very probable that this is the source of the testicular hormone. We cannot however be sure that the hormone is not made by the cells of the seminiferous tubules, as will be discussed later.
The genital duct system. When the sperm cells have reached completion in the testis, they are perfectly formed but inactive. Freed from their parent cells, they are swept passively along the tubules into the larger ducts that drain the tubule system. If the sperm cells were discharged from the body in this nonmotile state they could not fulfill their task of reaching and fertilizing the egg cell. They require a further period of ripening and conditioning until they become fully motile and potent. Furthermore the seminal fluid in which they are to be carried must be made and added to them, bringing suitable substances for their nourishment and stimulation.
These needs are served by a complex system of ducts and accessory glandular structures. The dozen or more ducts that leave the testis all drain into a single tube about 7 meters (21 feet) long, which is tightly coiled, as shown in Fig. 31, into a dense mass, the epididymis, which lies upon the testis. This coiled duct is lined by special secretory cells and is believed to function as a storage place for sperm cells, which take many days to be carried through its whole length. During this journey they have time to mature. If one examines under the microscope sperm cells taken from the epididymis of a freshly killed animal, they are found to be in active motion, whereas those taken from the testis are motionless. There has been a good deal of discussion, not yet settled, as to whether the activation of the sperm cells is brought about by stimulatory substances secreted by the cells lining the tube of the epididymis, or merely by the process of maturing. Regardless of this question, it is at least certain that the epididymis is a favorable place for the sperm cells, for when experimenters have tied off its tube in two places, leaving sperm cells trapped between the ligatures, the cells have been found to remain active for two weeks or more.
Emerging from its coiling in the epididymis, the seminal canal becomes less tortuous and finally runs directly upward under the skin toward the groin, as shown in Fig. 30. This part of the system is called the seminal duct or vas deferens. The two ducts (one from each testis), pass over the front of the pelvic bones to enter the interior of the pelvis. Proceeding down the side and rear of the pelvis the two ducts approach each other under the urinary bladder. Before they unite each of them gives rise to a small saccular offshoot or branch, the seminal vesicle. These vesicles are clubshaped hollow structures, really side branches of the seminal duct. They are each about 10 centimeters (4 inches) long, but folded to half that length as they lie in place. They are glands of external secretion, producing in their cavities a clear gelatinous substance which becomes part of the seminal fluid. There is an old notion, hardly yet cleared out of the medical textbooks, that the seminal vesicles are reservoirs for sperm cells, but the fact is that sperm cells are not normally found in them.
The whole course of each seminal duct from epididymis to their junction, is about 30 centimeters (1 foot) long. As shown in Fig. 30, the two ducts unite just below the bladder and enter the urinary channel, the urethra^ just after it makes its exit from the urinary bladder. The combined seminal and urinary channel then passes through the prostate gland and enters the penis.
The prostate gland. To most people the name of the prostate gland probably conveys no clear impression, but only a vague and slightly ominous suggestion of something one hardly speaks of unless it makes trouble. Years ago Mr. Henry Mencken, when a columnist on the Baltimore Sun^ wrote an amusing article on the relative respectability of the human organs. The heart and lungs, he said, are perfectly respectable, the liver not quite, the spleen dubious and the kidneys definitely vulgar. In those days the prostate gland was so far below the standard of respectability that it could not even have been mentioned in the newspaper. Possibly the fact that its prosaic name, from the Greek prostates ("standing before" the urinary bladder), is often confused with the word "prostrate" adds to its flavor of indignity.
This unjustly disparaged organ is actually a gland of external secretion. It consists of 15 to 30 branched tubular glands, imbedded in connective tissue and muscle, forming a round mass 20 grams (2/3 ounce) in weight and almost completely surrounding the urethra just below the urinary bladder. The branching tubules of the prostate gland deliver a special secretion to the spermatic fluid, about which we know very little except that it is favorable to the activity and function of the sperm cells.
The various portions of the duct system and accessory glands are connected through the autonomic nerves so that all of them contribute to the seminal fluid when it is ejaculated at the climax of sexual excitement.
The prostate gland is one of those organs which carry on their useful functions in complete silence, never making known their presence or their action as long as they are in good working order ; but when something goes wrong with one of them it suddenly becomes the focal point of the universe for the sufferer. Its bad reputation as a source of trouble in elderly men is due to the fact that for some obscure reason, probably of endocrine nature, the gland tends to enlarge in men past 50. Situated as it is around the urinary channel (see Fig. 80), and enveloped in a heavy capsule, which prevents it from swelling outward, any marked enlargement of the prostate inevitably blocks the outflow of urine, with serious consequences. The hope that prostatic enlargement may (when we know enough about it) be brought under control by treatment with hormones, lies temptingly before the investigators and may some day be realized.
Secondary sex characters. Before we can discuss the hormone of the testis we must take account of certain other matters that form part of the pattern of sex. Primarily a male animal differs from the female, or a man from a woman, because the one has in all his cells the chromosomes for maleness, the other the chromosomes for femaleness. One therefore develops testes, the other ovaries. The sex glands then begin, even in the early embryo, to call forth the secondary sex characters of their respective sexes. When the individual reaches the age of puberty these characters become prominent. In most mammals the males are larger, and possess heavier, rougher skeletons and stronger muscles. The shape of the pelvis, and to a lesser extent that of the skull and the other bones, is different in the two sexes. In humans the anatomy of the larynx is different and therefore the voice becomes either male or female. The distribution and growth of the hair are different. One sex has well developed mammary glands, the other only rudiments.
In the various divisions of the animal kingdom there is a vast array of secondary sex differences. The tail of the peacock, the antlers of the stag, the beard and the smell of the billy goat, are evidences of what Nature can do in this way. The subject would fill a large book.^ Perhaps the most familiar of all, the comb of Chanticleer, has been seized upon by the experimenters (as we shall see) and has been made to tell us, more than any other one sign, just how the hormones control the secondary sex characters.
THE HORMONE OF THE TESTIS
People have known since prehistoric times that castration of men and domestic animals suppresses the development of secondary sexual characters and causes atrophy of the accessory male sex organs, such as the seminal vesicles and prostate gland. The gelding of stallions, the castration of male calves to make steers, of cockerels to produce capons, and even of boys for the production of eunuchs, has long been practiced. If anyone asked how the testis can control the size and form of the skeleton, the distribution of hair, or the tone of the voice, the explanation was vaguely to the effect that some sort of "sympathy" existed between the parts of the body, with the implication that the nervous system is the connecting agent. In 1849, however, Arnold Adolph Berthold, a physician and zoologist of Gottingen, proved once for all that the influence of the testis is carried by something that travels in the circulating blood. Berthold's little contribution (it is only four pages long) belongs to the fundamental classics of endocrinology.' He tells us that on August 2, 1848, he castrated 6 cockerels, 2 to 3 months old. Their combs, wattles and spurs were not yet developed. From two of them the testes were completely removed. These became typical
2 See many, chapters of Edgar Allen, Sex and Internal Secretions. 8 A. A. Berthold, "Transplantation der Hoden," Archiv fur Anatomie, Physiologie, und Wissenschaftliche Medizin, 1849 (Appendix II, note 18).
{
THE MALE HORMONE
capons, fat, docile, without cocks' combs, wattles and spurs, unable to crow. In the case of two others, Berthold removed both testes but put one of them back, dropping it among the intestines. Anatomical examination months later showed that the reimplanted testes had become attached to the intestines and had acquired a good blood supply, so that the testicular tissue flourished in its new site. Both these cockerels became typical cocks ; they grew combs and wattles, crowed, fought their rivals, and, as Berthold delicately observes, "showed the customary attention to the hens." One of these was later opened surgically, the implanted testis was removed, and the comb and wattles cut off. The head furnishings did not regenerate, and the bird, now fully castrated, reverted to the status of a capon. The other two each had one testis removed, then Berthold exchanged the remaining testes, giving each bird the other's sex gland, which he implanted on the intestine. These also became typical cocks. This beautiful experiment showed that the testis by no means depends upon specific nerves to maintain its control of the secondary sex characters, but works through the blood.
A long story could be told of all the efforts that were made to follow up this discovery, and there would be many divagations to relate. There was, for example, the episode of Charles-Edward Brown-Sequard, a brilliant, restless FrancoIrish- American (181T-1894!), who made two incursions into the field of the internal secretions. In 1856 he was the first to remove the adrenal glands from animals and to observe the fatal disorder thus produced, like an exaggerated Addison's disease. In 1889, when he was seventy-two years old, he began to dose himself with extracts of dogs' testicles. He was feeling the debility of age, and hoped to rejuvenate himself. BrownSequard had been a good scientist and it is almost incredible that he could have hoped to do critical experiments with himself as the only guinea pig, prejudiced by all his hopes and fears for his own health. He thought that after the injections
{ 229 }
THE HORMONES IN HUMAN REPRODUCTION
he felt much stronger and more alert, and reported his experience with pathetic enthusiasm and intimate personal detail before the medical societies of Paris and in the journals. The medical profession was on the whole incredulous and Paris made a good deal of fun of him. We know now that the extract could have had little or none of the genuine testis hormone in it. It was made by putting mashed-up testes in water and filtering the mixture. We are now well aware also that when a man grows old he ages all over, not only in his testicles. Nevertheless the idea of administering gland extracts had its up-to-date appeal in those days of the earliest discoveries about the endocrine organs. German biochemists had recently isolated from animal testes a peculiar nitrogenous substance called "spermine." Various people leaped to the conclusion that this might be the active substance in Brown-Sequard's extracts. Spermine was therefore put on the market under the auspices of the chemist Poehl, and thus became (to the best of my knowledge) the first endocrine product to be commercialized. Thus Brown-Sequard's notoriety was probably responsible, more than anything else, for the exploitation of endocrine preparations in the drug trade ahead of scientific knowledge. Since then, barrelfuls of extracts and millions of tablets have been fed and injected into human patients, with uncritical optimism, before the chemists and physiologists could learn the facts. The benefits of endocrine research on the reproductive glands have almost been stifled by this exploitation. Even today the practicing physician finds it difficult to distinguish what is sound and practical amid the flood of well advertised endocrine drugs.
There have been premature efforts also to apply Berthold's experiment of transplantation of the testis to the rejuvenation of senile men. The most widely publicized of these was that of the Franco-Russian surgeon Serge Voronoff, who was busy from about 1912 to 1925 implanting monkey testes into human patients. The American journalists of those days
{ 230 }
THE MALE HORMONE
could not refer to the testicles by name in the newspapers, and introduced the expression "monkey glands," which became a byword and finally a joke. Some of the patients reported hopeful results. The grafts may indeed have yielded a little of their hormone to the body before they disintegrated and disappeared. More often, no doubt, the benefit was entirely psychic. It is now clearly established that tissues from one species of mammal cannot grow in another species, and indeed it is practically impossible to secure a permanent transplant from one human to another. Grafting of the testis has therefore not been adopted as a sound procedure.
While we are on the subject of rejuvenation, we may as well mention the Steinach operation. Eugen Steinach of Vienna, a scientist of good reputation, came forward about 1920 with a proposal based on two premises. The first of these, which has even yet not been proved, was that the testis hormone is made entirely by the interstitial cells. (The question will be discussed more fully below.) The second premise has since been proved incorrect; it was that if the seminal duct is tied off, the seminiferous tubules will degenerate leaving more room for the interstitial cells, and these will increase in number and presumably make more hormone. Steinach believed that such a ligation of the seminal ducts of man (vasectomy) would restore vitality of body and of sexual function to elderly men. He brought forward apparently strong evidence from animal experiments to support the idea. The operation made a strong appeal to men who were yearning to regain their lost youth. It has been tried widely, but the medical profession remains unconvinced, and the scientific basis for it as outlined above has been disproved.
Meanwhile, through all this period of sensationalism and premature publicity, the slow implacable attack upon the problem by inconspicuous investigators has gone forward to notable success. The important thing in endocrine research is
{ 231 }
THE HORMONES IN HUMAN REPRODUCTION
to find a test for whatever hormone one suspects to exist — some sharp-cut characteristic effect that is lost when the gland is removed and that can be restored by giving back the gland in implants or in extracts. At each step of our story in this book such a method has been the key to success. The vaginal smear test for the estrogens, the rabbit uterus test for progesterone, promptly made possible the purification of these substances. If the test is quick and cheap, the results will come that much faster. Berthold's experiment with the cockerels provided an ideal method of testing for a hormone of the male sex gland. Success came to those who followed his lead, putting aside premature efforts to work with slowly growing mammals or to rejuvenate old men. Between 1907 and 1927 two or three European investigators reported that they had extracts of the testis which induced growth of the head furnishings of cocks. None of these experiments, however, was fully convincing. Meanwhile the estrogenic hormones were isolated and discovered to be soluble in fat solvents. In 1927 a graduate student in biochemistry under Professor F. C. Koch at the University of Chicago, L. C. McGee (now a physician in Elkins, West Virginia) applied the new methods of extraction to the tissues of the bull's testis and promptly secured a relatively pure extract that was capable of producing rapid growth of capons' combs (Fig. 32). This lead was followed up by a group of workers in biochemistry and zoology in the University of Chicago, including McGee, F. C. Koch, C. R. Moore, L. V. Domm, and Mary Juhn, and by various workers abroad. The successive steps in the purification and identification of the male or androgenic hormones were much like those in the isolation of the estrogenic substances. In 1929, S. Loewe and S. E. Voss of Dorpat (Estonia) and also Casimir Funk and B. Harrow of New York found androgenic substances in human urine from males. The indefatigable Butenandt and his aides then
{ 232 }
THE MALE HORMONE
Fig. 32. The effect of testis hormone on the rooster's comb, a, untreated castrated cockerel. 6, castrated cockerel after 11 days' treatment with testis extract. Drawn from photograph by Freud and coworkers.
isolated, completely purified and identified two of these compounds, called respectively androsterone and dehydroandrosterone, in 1931-1932. L. Ruzicka and his colleagues at Basel made them synthetically in 1934. The next year David, Dingemanse, Freud and Laqueur of Amsterdam succeeded in the difficult task of purifying the hormone from extracts of the testis itself, and found the substance called testosterone, which differs slightly in its chemical constitution from the androsterone found in urine. The groups of workers led by Butenandt and Ruzicka immediately synthesized this hormone as well. Now that such substances could be made in the test tube as well as in the testis, and (as we shall see) began to be found in other tissues also, the adjective "male" as applied to them gave place to the more apt word "androgenic," meaning "promoting masculinity"; the latter word defines the effects without implying any particular place of origin and can therefore be used of such substances when, for example, they turn up in female urine, in the cortex of the adrenal gland, or in a chemist's flask.
Chemistry of the androgenic hormones. These substances belong to the same family of chemical substances as the estro
{
}
THE HORMONES IN HUMAN REPRODUCTION
genie hormones and progesterone. Testosterone has the following structure :
CH3 ^OH
TESTOSTERONE
Androsterone, prepared from human male urine, has this formula :
ANDROSTERONE
A statement of the relation of these particular sterols to simpler chemical substances will be found in Appendix I.
At the present time at least thirty-five substances of similar composition are known which have androgenic effects. Some of these have been found in the adrenal gland, or in the urine under special circumstances, but most of them are artificial products of the chemical laboratory. A list of them is given by Koch.* The male hormone which is actually at work in the body is probably testosterone itself or a closely similar substance. The reason a definite statement cannot be made on this point is that we are not sure that the chemical procedures necessary to extract and concentrate the hormone do not change it chemically. When testosterone is administered to a castrated animal, it is transformed in the body and is excreted by the kidney as androsterone. Since androsterone occurs in the urine of normal men, this is presumptive evi
Edgar Allen, op, cit.. Chapter XII, "The Biochemistry of Androgens," by F. C. Koch.
THE MALE HORMONE
dence that testosterone, or something very much like it, is in circulation in the body.
Just what cells in the testis are responsible for producing the hormone is an interesting and debatable question. There are two possibilities, the interstitial cells on one hand, and the spermatogenic cells of the tubules on the other. Let us examine the evidence. In the first place the interstitial cells look like endocrine tissue, since they are large cells provided with a rich circulation of blood but obviously not producing an external secretion, for they are not arranged in channels and ducts. Years ago, moreover, Bouin and Ancel called attention to evidence favoring the interstitial cells as the source of the hormone. When the testes fail to descend and therefore do not form sperm cells, the cells lining the tubules are reduced to an inactive state (Plate XXIV, B). They assume a vague, nondescript form as if they were merely surviving without any function. The interstitial cells however remain in place, they look normal, and indeed have even been thought to increase in amount. Although the cryptorchid animal or man bearing such sex glands is sterile, he develops male secondary sexual characters and male sex psychology. With the spermatogenic cells seemingly inactive (as judged by appearances under the microscope) but the interstitial cells in good condition, it is difficult to avoid the assumption that the latter are making the sex hormone. When bits of the testis are grafted successfully into a castrated animal the same cellular state develops in the grafts, and the animal likewise develops male qualities. It was formerly thought that tying off the seminal ducts produced the same effect. The Steinach operation described above was based upon this whole set of considerations. It is now known, however, that blocking the ducts and thus damming up the semen does not stop spermatogenesis. It is also known that cryptorchid (undescended) testes with inactive sperm cell formation do not
{ 235 }
THE HORMONES IN HUMAN REPRODUCTION
produce more hormone but considerably less. In short, the two functions of the testis, spermatogenesis and hormone production, run parallel to a certain extent. For this reason some of the soundest of the investigators are not willing to point to one or the other of the constituent tissues of the testis and saj^ "here is the sole source of the hormone." The tubule cells, even if they are inactive in producing sperm cells, may for all we know still be taking part in making the hormone ; or perhaps the two kinds of cells work together. If a time ever comes when the hormone can be recognized in the tissues in very small amounts, say by some sort of super-spectrograph or X-ray analysis, such as the modern magicians of the physics laboratories are using in their easier problems of test tube chemistry, then perhaps we can answer such questions as these.
There is no sharp division between the estrogens, the androgens, and the progestins. Several of these substances give both estrogenic and androgenic effects, and a few have been found even to affect the uterine lining like progesterone, though only in very large doses.
The androgens are usually assayed by testing their effect upon the growth of the comb of the capon. The League of Nations Committee on Standardization of Drugs set up in 1935 an international standard of potency, specified as the equivalent of 0.1 milligram of crystalline androsterone. This is approximately the daily dose required to give a measurable response in a capon's comb in 5 days.
The androgenic hormones are usually injected in oil solution. In recent years the method of implanting pellets under the skin has begun to be tried. The hormones are also effective when applied in suitable ointments. Growth of the cock's comb can be elicited by applying hormone-containing ointments directly to the comb itself (Appendix II, note 19).
Effects and medical use of the androgenic hormones. The
{ 236 }
THE MALE HORMONE
effects of the androgenic hormones, as C. R. Moore" neatly puts it, are measured by the difference between a castrated and a normal man. These substances substitute completely, in animal experiments, for the normal internal secretion of the testis. They counteract castrate atrophy of the seminal vesicles and prostate gland ; when given to immature animals they stimulate precocious growth of the accessory sex organs, and they induce sex activity and mating in castrated and immature males. A castrated male, skillfully treated with potent hormones, will resemble a normal animal of his species in all respects except that he will be infertile because he is producing no germ cells.
These effects have been tested quite thoroughly in an experimental way upon human patients who lack the testis hormone. In these men and boys, as in laboratory animals, the injected hormones bring out all the known responses which the bodily tissues normally make to the natural hormones of the testis. It should be recalled here that the symptoms of deprivation of testis hormone may be due to defects in either one of two glands. The testes may themselves be missing or deficient, or the pituitary gland may be furnishing an inadequate supply of gonadotropic hormone (see Chapter VI). In the latter case the testis will not be functional and the patient will show symptoms of testis hormone deficiency exactly as if the testis itself were the seat of the difficulty. At some time in the future, when endocrine treatment has reached a higher state of perfection, it may become possible to treat the pituitary cases with pituitary hormones, reserving the androgenic hormones for cases of deficiency of the testis itself. At present, however, the distinction is more or less academic. In either case the physician finds himself confronted with signs of male hormone deficiency, and the question of immediate importance is how
8C. R. Moore, "Physiology of the Testis," in Glandular Phytiology and Therapy , 2d ed., Chicago, 1942.
{ 237 }
THE HORMONES IN HUMAN REPRODUCTION
far he can hope to help the patient by treatment with androgenic hormones.
I write about this subject of the medical use of the androgenic hormones with hesitation, because it is difficult on one hand to avoid raising false hopes without on the other hand underrating the progress that has been made and the future possibilities in this field. To make the problem clearer, let us consider a specific case.® Here is a boy in his middle 'teens who is not exhibiting the usual signs of sexual maturation. We know that if the deficiency persists he will grow to be a eunuchoid man. He will have underdeveloped genital organs, a delicate skin, the childhood type of hair distribution, a highpitched voice; possibly also he will be overfat and he may suffer from muscular and circulatory difficulties causing easy fatigability and inability to do hard muscular work. Another important feature of his general immaturity will show itself in the long bones of the skeleton. The growth zones (epiphyseal junctions) will not close up at the usual time (18 to 20 years), but will go on growing, so that he will develop the long delicate bones of the eunuch and will thus display his defect in the entire configuration of his body. Although the deficiency has nothing to do with intelligence or fundamental character, he is very likely, as he grows up, to suffer from psychological damage due to a sense of defectiveness and of difference from other men.
If this boy could be treated as simply as a guinea pig is treated in the laboratory, we could control all these visible defects by administration of androgenic hormone. The treatment is fairly expensive and must be kept up by frequent injections or inunctions. Administration by pellets buried in the tissues may in time become practical, but is hardly yet ready for use. We are, moreover, not yet free from insecurity about possible danger from long continued administration of
ej. B. Hamilton, "Testicular Dysfunction," in Glandular Physiology and Therapy, 2d ed., Chicago, 1942.
THE MALE HORMONE
the sex hormones through damage to the tissues of various organs. Finally, whatever improvement is gained by treatment will wear off fairly rapidly if the drug is discontinued. In one feature only, so far as known, the improvement is permanent; that is in the skeleton, for the growth of the long bones will be permanently stopped by closure of the epiphyseal junctions. Even this requires care and forethought, for if the treatment is begun too early, the epiphyses may be closed prematurely and growth stopped before the boy reaches full stature.
I have no doubt said enough to make it clear that the use of androgenic hormones to correct testicular hormone deficiency is very decidedly still in the stage of exploration, and that every case so treated is an experiment. This does not mean that the attempt should not be made by properly trained physicians and scientists who are in a position both to guard the welfare of the patient and to study the results with rigid scientific standards for future guidance. We have, of course, been considering an extreme case, one in which there is permanent total deficiency. The androgenic hormones are certainly going to be useful in many disturbances of less intensity and as collateral treatment. To make up for partial deficiencies, to tide over the acute deprivation which follows surgical removal of the testicles, to supplement the treatment in various cases of sexual disability and impotence — for such purposes the androgenic substances will no doubt be helpful in competent medical hands.
At any rate, the contemplation of these distressing deficiencies of the sex hormones must have impressed the reader anew with the thought that the normal processes of reproduction involve a remarkable series of linkages and coordinations within the body. It is indeed a subtle and potent chemistry by which the reproductive glands create the egg and the sperm cell and surround them with all that is needful of nourishment and protection to carry them through their critical journey from conception to birth. In this book we have traced the main outlines of these complex physiological patterns. We have seen the great advance of knowledge that has taken place in less than fifty years, by the efforts of faithful laborious men who worked in peace and quiet, giving their lives to the understanding and improvement of life. When I wrote these closing words, the guns were sounding all over the world. The scientists were dropping their instruments, or turning them perforce to the uses of death and wastage. But life goes on nevertheless, and the problems of life will be studied until the day comes we all dream of, when mankind may everjrwhere seek the truth undaunted by fear of war and oppression. In that day we shall gather the fruits of our labor. The childless wife, the ailing girl, the boy deprived of his birthright of sex by some failure of Nature's process, will call and not in vain for the help that science can bring them, and man shall understand at last the miracle of his birth.
