An autoradiographic study of long-term follicular development in the cyclic hamster.

The time required for ovarian follicular development in the cyclic hamster was determined by marking follicles with [3H]-thymidine on day 1 of the estrous cycle (day of ovulation) and by following their fate over the next three cycles by autoradiography. A model of follicular development was formulated, based on the total number of follicles and the changing percentage of labelled follicles with time. It was estimated that 20 days elapsed before a preantral follicle with two to three layers of granulosa cells (stage 1) was able to ovulate. Follicles spent eight days in stage 1 and an additional eight days in stage 2 (4-5 granulosa layers). Preantral follicles entering stage 3 (6-7 granulosa layers) and 4 (greater than 8 layers) on day 1 of the cycle ovulated four days later. Approximately 30 follicles per ovary entered and left stage 1 each cycle, representing a 50% turnover. Of the follicles leaving stage 1, about 50% were transformed into stage 2 follicles; the remaining ones underwent atresia. Stage 2 follicles also had a 50% turnover each cycle. Half of the stage 2 follicles underwent atresia; the remainder developed into stages 3 and 4 follicles. Fifty percent of the stages 3 and 4 follicles present on day 1 of the cycle ovulated at the next estrus with the remainder undergoing atresia.