Acute effects of unilateral ovariectomy on follicular development in the cyclic hamster

Hamsters were hemispayed at 09:00 h on Day 3 of the cycle (Day 1 equal to ovulation) and were killed 1 h after injection of [3H]thymidine at 09:00, 12:00, 17:00 or 22:00 h. Unilateral ovariectomy had no effect on the number of Stage 1 or Stage 2 follicles, but there were significantly fewer Stage 3 follicles between 10:00 and 13:00 h. This decrease was not encountered in intact hamsters and was reflected in an increase in the number of Stage 6 (antral) follicles. At 13:00 h there was no difference in the number of atretic follicles between the experimental and control groups. It is concluded that preantral follicles with 6-7 layers of granulosa cells were recruited within 4 h after unilateral ovariectomy and transformed into antral follicles.