Age-Related Morphologic and Microscopic Variations in Syrian Hamster Ovaries and Oocytes.

Factors contributing to age-related decline in fertility rate include quantity and quality of follicles and their associated oocytes and their responsiveness to reproductive hormones. Mitochondria and smooth endoplasmic reticulum are purportedly components of oocyte cytoplasmic senility. We have evaluated ovarian follicle number and egg production and the microscopic variations in mitochondria and smooth endoplasmic reticulum (SER) between young (2-4 mos.) and old (12-18 mos.) Syrian hamster oocytes. Experimental animals were superovulated by intraperitoneal injections of pregnant mare serum gonadotropin followed at 54 hrs by human chorionic gonadotropin 8-14 hrs prior to the collection of ovaries and oocytes. At eight hrs, ovaries were collected for primordial/primary follicle counts. At 14 hrs oocyte masses were collected for microscopic analysis. Hematoxylin and eosin staining of ovarian tissue from two animals evaluated through serial sections established a 67% decrease in primordial/primary oocytes in old versus young hamster ovaries. Primordial/primary follicles contained a germinal vesicle and either a single layer of squamous epithelial cells or one to three layers of cuboidal epithelial (granulosa) cells without follicular antra. A 30% reduction in oocyte number was collected from superovulated old (avg. 20.9, n=45) versus young (avg. 29.8, n=42) hamsters. Comparing the ultra structural components of oocytes superovulated from young and old hamsters showed young hamsters having more mitochondria and smooth endoplasmic reticulum (SER) than old hamsters as seen in other species. All oocyte mitochondria had large amounts of electron dense areas, also seen in other species, but old ova had reduced number of distinct cristae and an increased electron dense mitochondrial area. Young ova had no collapsed SER while old ova were replete with areas of collapsed, non-luminal SER. The non-luminal stretches of SER were adjoined to and contiguous with the normal-looking SER strands in the old oocytes. Evaluating ova from 3 young and 4 old females under 32x magnification, 89% of young ova were predominantly expanded against the zona pellucida (no perivitelline space) with a clear indentation at the polar body while 48% of old ova could be described in this way. The remaining old ova had increased perivitelline space with no indentation from the polar body. In conclusion the results not only support the theory of oocytes depletion as aging occurs, but also suggest morphological changes of mitochondria and SER in oocytes may be attributing factors in the age-related decline in fertility rate. This research was supported by The Jones Institute Foundation and the Department of Obstetrics and Gynecology of the Eastern Virginia Medical School. (poster)