Paper - Growth of the reproductive and endocrine organs of the guinea-pig (1936)

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Deanesly R. and Rowlands IW. Growth of the reproductive and endocrine organs of the guinea-pig. (1936) J Anat. 70: 331-338. PMID 17104594

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This 1936 paper by Deanesly and Rowlands describes guinea-pig genital and endocrine development.

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Growth of the Reproductive and Endocrine Organs of the Guinea-pig

By Ruth Deanesly and I. W. Rowlands

From the National Institute for Medical Research, Hampstead


During the last two years, a large number of normal guinea-pigs have been killed in this laboratory to obtain control material for various experiments on the reproductive and endocrine organs. The material now covers a wide range of body weight, and in the absence of any extensive information of this kind for the guinea-pig, such as H. H. Donaldson (1924) published for the rat, the data seem worth recording. Ibsen (1928) gave details of pre-natal growth in the guinea-pig, but did not deal with post-natal growth, other than that of the pregnant female. Moore (1982) described the effects of gonadectomy on the weight of the accessory organs of a small group of male and female guinea-pigs, compared with an equal number of normal controls. Kosaka (1932) analysed the relations of cortex and medulla in the adrenals of sixteen adult guinea-pigs and reports that the left gland is always larger than the right.

No attempt is made here to deal with the histology or functional activity of the reproductive and endocrine organs of the guinea-pig, since numerous papers on these subjects have already been published.

Material and Technique

Animals. One hundred male and ninety-one female guinea-pigs were examined. The males ranged in body weight from a little over 200 gm. to a little over 700 gm.; the females from 170 to 700 gm. The body weights recorded (B.w.) are those of the intact animals, of which the great majority were from the inbred colony maintained at the Institute’s Farm Laboratories. Some animals from other sources were included for completeness.

Preservation and weighing. The reproductive organs and the thyroids and adrenals were removed from each animal and fixed in Bouin’s fluid and upgraded to 70 per cent. alcohol. The testes, seminal vesicles, ovaries, thyroids and left and right adrenals were then weighed on a torsion or chemical balance. The epididymis and prostate were not weighed, being difficult to dissect accurately in the guinea-pig. Weighing after fixation was unavoidable in the case of the seminal vesicles, which are distended with fluid in the fresh condition, and it was convenient for the other organs. Occasionally, however, some were damaged or put into different fixatives and not weighed, so that the available data for the separate organs are slightly fewer than the total numbers of animals.

Treatment of results. The results are shown in the form of scatter diagrams. No mathematical treatment has been attempted, except for the thyroids (Rowlands and Parkes, 1984), although in several cases the organ weights bear an obvious linear relation, or two successive linear relations, to the body weight, and the calculation of regression lines would have been a simple matter. The additional accuracy obtainable, however, by this as compared with graphical methods, would be of no value in the circumstances.


Fig. 1 gives the scatter diagram for the weights of the paired testes which show three fairly distinct phases of growth. At B.w. under 300 gm. the testes are small, mainly below 0-5 gm., and the rate of increase is slight. From

Fig. 1. Weight of the testes in the guinea-pig.

800 to 400 gm. B.w. there is rapid growth, until the testes reach an average of about a little over 2 gm. From this point, growth is slower, but, nevertheless, the testes may approach a weight of 4 gm. in large guinea-pigs of over 800 gm. The variation in testis size is not unduly great considered in relation to variations in B.w.

Seminal Vesicles

The scatter diagram for seminal vesicle weights is given in fig. 2. The seminal vesicles, instead of remaining undeveloped during the early growth of the testes, as in some other species, begin to enlarge at about the same time as the testes. At B.w. below 300 gm. the seminal vesicles are small, generally below 0:25 gm., but thereafter their development is rapid. From 300 to 350 gm. B.w. they may weigh anything from 0-1 to 1-5 gm., showing a wide range of variability even for a rapidly growing organ. This gross variability increases comparatively little as the B.w. goes up to 600 gm., so that the percentage variability actually decreases. In about 600-gm. guinea-pigs and larger ones, however, the weights observed were extremely variable, roughly from 1 to 10 gm. Only two conclusions can be drawn from these data: (a) that the vesicles are normally small and undeveloped below 800 gm. B.w. and -b) that only in animals of over 500 gm. B.w. is there a reasonable certainty that the vesicles are well grown.

Fig. 2. Weight of the seminal vesicles in the guinea-pig.


The scatter diagram for ovary weights is shown in fig. 3. The general trend is very similar to that of the testes. From 150 to 300 gm. B.w. the ovary weight is remarkably steady, being about 50 mg., with a gross variation of © t+about 15mg. Between 300 and 400 gm. B.w. the ovaries may increase appreciably in weight, but many as low as 50 mg. are still found. Above 450 gm. B.w. the numbers are inadequate for drawing conclusions.

The onset of ovarian activity, as diagnosed by weight, at 300 gm. B.w. obviously corresponds to the start of the oestrous cycle. The smallest pregnant animal weighed 340 gm. The rise in ovary weight at puberty, however, is not nearly as steep as in the rat (H. H. Donaldson, 1924), where the corpora lutea form a larger proportion of the ovary. It is very noticeable in these records that the ovaries of pregnant animals are no larger than those of non-pregnant, even allowing for the slight misplacement of the animals in the weight scale; this would be expected from the small size of the corpora lutea of pregnancy (Deanesly and Parkes, 1931). 334

Weight of ovaries mg.

Weight of thyroids mg.


e e 150 e ° e

° ° © e e 100 F : © e e oe e e “oe @ e ° Pe sep Oe, ° @ 50 f « of 0°, @& eos 9808, e eo, & ° e ° 700 200 300 400 500 600 700 800 Body weight gm. Fig. 3. Weight of the ovaries in the guinea-pig. @ non-pregnant; © pregnant. 120 e e 100F e e e e ® 80 ee ee e.° * 60 e e e e e ® e 3 ° e Se e ° e e e 40F e e e og**e coe ° e 20+ e 1 4 1 4. 1 1 1 —L° 100 200 500 600 700 800

200 400 Body weight gm. Weight of the thyroids in the male guinea-pig.


The thyroids of the males are plotted in fig. 4 and those of the females in fig. 5. Growth in the female up to 300 gm. B.w. has been dealt with by Rowlands and Parkes (1984), who found that the obviously linear relationship could be expressed by the formula y =0-159x—1-02, where e=B.w. in gm. and y= weight of the thyroids in mg., i.e. that the thyroids increased about 1 mg. in weight for every 6 gm. B.w. In the male, a good linear relationship is found up to 350 gm. B.w., with a very similar slope and position to that found in the female. In the female above 300 gm. and the male above 350 gm.

Fig. 5. Weight of the thyroids in the female guinea-pig.

B.W. the points fan out so greatly that it is difficult to draw conclusions except that the thyroid of the adult guinea-pig is very variable. A male guinea-pig of 700 gm., for instance, may have thyroids only half the size of another

guinea-pig of only 450 gm. ADRENALS Male guinea-pigs. Separate scatter diagrams are given for the left and right adrenals. Those for the male (figs. 6 and 7) provide two definite con clusions: (a) Adrenal weight bears a linear relation to B.w. Over the wide range of B.w. examined each adrenal increases by about 4 mg. for each 10 gm. increase in (b) The left adrenal is slightly but consistently heavier (10-20 mg.) than the right adrenal (cf. Kosaka, 1982). This is also true of the rat (J. C. Donaldson, 1919). ,

Fig. 6. Weight of the right adrenal in the male guinea-pig.

Fig. 7. Weight of the left adrenal in the male guinea-pig.

Female guinea-pigs. The scatter diagrams for the adrenals (figs. 8, 9) show that their growth is rather different in the female, although, as in the male, the left adrenal is the larger. There is a definite acceleration in the growth of both adrenals when the B.w. reaches 320-340 gm.; i.e. at exactly the same

300 oo a a e 4 e 200) e e a % & e H e 3 ee e ° 3s ee) = 1 BS ° . e stead oe e e 088, ° 700 200 300 700 500 600 700 Body weight gm. Fig. 8. Weight of the right adrenal in the female guinea-pig. 500F e 4001) a e @ soot ° 3 6 200F ° we 3 © ae 2 e e e = te cy O00 c 100 + a Bee § e oS eo e Ce”. eo. “ee” 100 200 300 400 500 * 500 700 Body weight gm.

Fig. 9. Weight of the left adrenal in the female guinea-pig.

B.w. as that associated with the sudden increase in the ovaries. Adrenal growth therefore seems to accompany the attainment of sexual maturity when the pituitary becomes more active. Apparently, however, there is no appreciable increase in adrenal weight during pregnancy (cf. J. C. Donaldson, 1924).


The growth of the testes, seminal vesicles, ovaries, thyroids and adrenals has been studied in a large series of normal guinea-pigs.

We are indebted to Miss M. Allanson, Ph.D., of King’s College, London, for assistance with the dissection and weighing of the organs.


Deraneszy, R. and Parkes, A. S. (1931). Proc. roy. Soc. B, vol. crx, p. 196.

Donatpson, H. H. (1924). “The rat.” Mem. Wistar Inst. vol. vt.

Donaxpson, J. C. (1919). Amer. J. Anat. vol. xxv, p. 291.

—— (1924). Amer. J. Physiol. vol. txvut, p. 517.

IssEn, H. (1928). J. exp. Zool. vol. ut, p. 51.

Kosaka, Y. (1932). Folia anat. japon. vol. x, p. 601.

Moore, C. R. (1932). Biol. Bull. Wood’s Hole, vol. xLit, p. 285.

Row tanps, I. W. and Parkes, A. S. (1934). Biochem. J. vol. xxviu, p. 1829.

Cite this page: Hill, M.A. (2024, June 23) Embryology Paper - Growth of the reproductive and endocrine organs of the guinea-pig (1936). Retrieved from

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