Paper - On the effect of removal of the pronephros of the amphibian embryo (1916)
Embryology - 23 Apr 2024    Expand to Translate
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Howland RB. On the effect of removal of the pronephros of the amphibian embryo. (1916) Proc. Natl. Acad. Sci. U.S.A 2(4):231-234. PMID 16586615
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On the Effect of removal of the Pronephros of the Amphibian Embryo
By Ruth B. Howland
Sweet Briar College, Sweet Briar, VA. Received by the Academy, March 9, 1916
The following note embodies the results of a series of experiments, performed at Yale University at the suggestion of Dr. R. G. Harrison, on embryos of the spotted salamander, Amblystoma punctatum. The particular problems in mind were first, to determine whether the head kidney or pronephros is a functioning organ necessary to the life of the embryo, and second, to investigate the correlation of the development of this organ with that of other components of the excretory system.
The embryos used for the experiments were nearly of a uniform age, varying slightly in size and degree of development from the condition in which the first loop of the pronephric tubules appears as a slight, ventrally directed curve of the duct, to the stage in which the two funnels, together with the first loop, appear as a broadened Y. (Fig 1.) The tail-bud was clearly defined, and the pronephric swelling distinctly visible. In all cases, however, embryos were used before contraction of the body muscles began, for contraction not only hindered the operation, but often tore open the wound after successful removal of the kidney.
Two methods were employed in removing the pronephroi. In the first, three straight cuts were made, one beneath and one along each side of the pronephric prominence. The flat of skin thus defined was lifted up and the organ removed from below. In the second and more satisfactory method, a single incision was made dorsal to or immediately over the thickening, the needle inserted, and the tubule raised upward from the ventral side and excised.
. ‘Conditions ensuing upon the removal of the head kidney of both sides in Amblystoma larvae show clearly that these organs are necessary to the life of the embryo, although the presence of one pronephros suffices to keep the organism alive and in a healthy condition. All embryos from which both head kidneys had been excised died within eight to twelve days, evidencing during that interval symptoms of weakened heartaction—oedema and effusion into the pericardial and abdominal cavities—presumably
FIG. 1—AMBLYSTOMA EMBRYO IN THE OPERATING b ‘ought about by ure STAGE, SHOWING THE PRONEPHROS EXPOSED AFTER RE- mic poisoning. Prick MOVAL OF ECTODERM. xX 13. ing the body wall to relieve the dropsical condition was resorted to in many cases from five to seven days after operating, but it proved ineffective.
The pronephros remaining after the removal of one head kidney evidently takes over the function of excretion usually performed by the two organs, and, concomitant with the increased physiological activity, presents marked morphological changes. The size of the organ which functions alone is greatly increased, indicating the occurrence of compensatory hypertrophy. In the normal pronephros, the walls of the tubules are thick, and consist of cuboidal cells, the central ends of which often bulge out into the narrow lumen. The hypertrophied tubules are thin walled, the cells flattened as is the case in normal larvae of greater age, and the lumen accordingly is nearly twice that of the unoperated specimen. To determine the nature and extent of the change brought about in the functioning pronephros through the removal of the organ on one side, wax models of this organ (X 200) of an operated specimen and of a normal embryo were constructed. The control was chosen from a large number of normal embryos which, on sectioning, showed the several organs (retina, lens of eye, digestive tract, etc.) to be in a stage of development identical with that in the operated individual. On comparison of the models, the evidence of hypertrophy shown in microscopic examination was strengthened. The model of the operated individual not only showed a considerable increase in length of the coiled tubule as contrasted with the control, but by its size indicated a great increase in volume. The length of the tubules making up the models was determined by taking the average of five measurements. The larger model measures 188 cm. (X 200), the smaller model 155 cm. (X 200), showing an increase of 21 per cent over the normal conditions. Difference in weight also indicates hypertrophy, the normal model weighing 62.9 gr. as contrasted with the larger, which has a weight of 115.9 gr.
The formation of the pronephric glomeruli under normal conditions as outgrowths from the aorta toward the newly forming kidneys suggested the possibility that in the operated specimens the glomeruli of one side might be lacking. The removal of one pronephros has, however, no effect on this development, for in all of the operated embryos both glomeruli were present. The glomerulus on the operated side is not as uniform in size and shape as the normally functioning one, its form evidently being largely determined by the width of the coelomic cavity in this region. The outer layer of the glomerular capillaries and the epithelial lining of the body wall often coalesce. Absence of the pronephros enlarges the cavity on that side, and the glomerulus is then found bridging this cavity as a long strand instead of appearing as a more compact tuft of capillaries.
In the removal of the embryonic pronephros, as much of the tissue was scraped out as seemed possible without disturbing the Anlage of the aorta. In spite of this fact, a large number of the operated embryos possessed well developed anterior and posterior nephrostomes and portions of the funnels, indicating that these structures are probably regenerated from the adjacent coelomic epithelium. Of the sixteen embryos examined, twelve showed well formed anterior funnels and nine had posterior funnels. In one instance the anterior funnel was of a peculiar double form, suggesting the normal condition in those amphibia with three pronephric openings.
The effect of excision of one pronephros on the formation of the segmental duct on the operated side varied widely. The process of development of the non-functioning ducts is carried on only to a limited extent. In the embryos examined, every gradation of development was found from a condition in which the lumen, though small and flattened dorsoventrally, appears throughout the entire length, to a condition where only the occasional presence of a few degenerating cells indicates the location of the atrophied duct.
Increased activity of a single kidney also has a definite effect on the segmental duct of that side. Cross sections of the duct of an individual with unilateral operation, when compared with either of the ducts of a normal larva of the same stage, show a marked increase in diameter.
The mesonephroi of both sides develop normally, at least in the early stages, even after excision of one pronephros. Non-development of the segmental duct in one instance left the mesonephric tubules disconnected on that side, and with no outlet for excretory products. No specimens have yet been kept a sufficient length of time to determine the ultimate outcome of this abnormal condition.
In brief then, the following conclusions may be drawn.
- Removal of both pronephroi in Amblystoma larvae induces conditions leading to oedema and subsequent death, though the presence of one head kidney is sufficient to keep the embryo in a condition of health.
- Excision of one head kidney brings about an increase in size in the remaining organ, and also in the diameter of the segmental duct on that side.
- Removal of one pronephros has no essential effect on the development of the pronephric glomerulus of that side, but the segmental duct appears in varying stages of atrophy.
- Anterior and posterior nephrostomes may regenerate from the coelomic epithelium.
- Early developmental stages of the mesonephros are. normal, even after excision of one head kidney.
Cite this page: Hill, M.A. (2024, April 23) Embryology Paper - On the effect of removal of the pronephros of the amphibian embryo (1916). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_On_the_effect_of_removal_of_the_pronephros_of_the_amphibian_embryo_(1916)
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