Development of preovulatory follicles and oocytes during the oestrous cycle of mature and aged rats

Publisher Website
Google Scholar
Abstract
The percentage of viable granulosa cells and the viability of the oocyte of each antral follicle on each day of the estrous cycle of mature and aged rats was determined by trypan blue exclusion and fluorescein diacetate assays, respectively. In mature rats, the number of mid-sized follicles (350-550 .mu.m in diameter) increased from estrus through diestrus. The percentage of viable granulosa cells increased in only mid-sized follicles which contained a viable oocyte. On proestrus, 2 types of preovulatory follicles (> 550 .mu.m in diameter) were observed in the mature proestrous rat: those with a high granulosa cell viability (> 60%) and a viable ooctye and those with a lower percentage of viable granulosa cells (< 50%) and a non-viable oocyte. Evidently, in mature rats only viable oocytes would be ovulated since presumably, only those preovulatory follicles with a high percentage of viable granulosa cells are able to ovulate. In aged rats, preovulatory-sized follicles were present on each day of the cycle. The percentage of viable granulosa cells within those preovulatory-sized follicles with nonviable oocytes increased on metestrus, decreased on diestrus and increased by proestrus. This pattern resulted in the development of 3-4 preovulatory follicles per ovary with all preovulatory-sized follicles possessing a high percentage of viable granulosa cells regardless of the functional state of the oocyte. In aged rats, all the preovulatory follicles apparently would ovulate but many of the ovulated oocytes would be defective. This mechanism would account for the lower fertility of these older animals.