Structure and Mechanism of Ovulation in the Golden Hamster: A Light and Scanning Electron Microscope Study

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Female golden hamsters were injected with 25 IU hCG on day 3 of a 4 day cycle to synchronize follicular development with ovulation expected 14 ± 2 h after hormone injection. Sectioned and intact ovaries and follicles were examined with light and scanning microscopes during the ovulatory process, and the following series of ovulatory events was described: 1. Sometime between hormone injection and 10 h, the apical wall of the follicle, including both thecal and granulosal elements, had thinned. 2. Beginning at about 10 h, a basal constriction could be detected. 3. By 12 h, the constriction was pronounced, and the lateral walls of the follicle were drawn inward thereby partially obliterating the antral space and pushing the fluid contents outward toward the apex. 4. In addition to the thinning of the apical wall, the surface epithelium also became separated; by 10 h, folded and stretched epithelial cells were seen as well as denuded areas where underlying areas were exposed. 5. As the basal constriction proceeded, antral fluid penetrated and further separated the thinned components of the apical wall. 6. The combination of basal constriction together with the thinning apical wall and separating surface epithelial cells further weakened the apical wall and produced a rupture. 7. Once a rupture had formed, the weakened apex collapsed inward forming a concave depression. 8. Continued basal constriction force the antral fluid against the apex causing leakage of fluid and granulosa cells from the depressed region followed by expulsion of the oocyte and cumulus mass. Our results clearly implicate a contractile mechanism functioning in hamster ovulation and suggest that the pressure applied against the non-compressible antral fluid plays a major role in the formation of the rupture necessary for the exit of the oocyte. (Supported by a grant-in-aid of research from the American Philosophical Society.)


Presented at the 96th Session of the American Association of Anatomists, Atlanta, GA.



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