Ovulation from rat and hamster ovaries in vitro.

The ovaries of pro-oestrous rats (pubertal and adult) and hamsters were explanted in toto at various times after the preovulatory gonadotrophin surge to obtain endogenously stimulated ovaries. Subnormal numbers of ovulations from pubertal and adult rat ovaries were found when incubation was started during the period from 17:00 to 24:00 h on the day of pro-oestrus. Normal numbers of ovulations only occurred from rat ovaries in vitro when incubation was started at 01:00 h, i.e. when ovulation had already begun in vivo. In contrast, full ovulation from hamster ovaries was observed in vitro after incubation at 22:00 h and later, although the ovulatory process had not started in vivo. This difference in the ability of rat and hamster follicles to ovulate in vitro could be due to a different role of the accumulation of tissue fluid for the mechanism of ovulation.