SOME MORPHOLOGICAL AND HORMONAL ASPECTS OF OVULATION AND SUPEROVULATION IN THE RAT

In the first experiment, mature female Wistar rats, displaying a regul ar 4-day oestrous cycle, were killed in succession every 2 or 3 h on t he day of pro-oestrus and oestrus until the time of ovulation. In the second experiment, immature female Wistar rats (aged 24 days) were inj ected s.c. with 30IU pregnant mare serum gonadotrophin (PMSG) and 56 h later with 20 IU human chorionic gonadotrophin (hCG). They were kille d in groups at 0, 24, 48, 56 and 57 h, and then every 2 h until 72 h. Excised ovaries were homogenized and analysed for steroid content or t hey were submitted to a routine histological procedure. The cyclic and PMSG/hCG-treated rats exhibited some similarities and differences in the general pattern of steroid content. Either a presumptive endogenou s LH surge or administration of hCG resulted in an increase in the ova rian androgen concentration which preceded a rise in progesterone; the progesterone peak, in turn, was accompanied by a fall in the amount o f androgens and oestradiol. However, in comparison with cyclic rats, s uperovulated animals displayed a significantly higher ovarian androgen level for a prolonged period; ovarian oestradiol concentration was al so raised while the progesterone content was much lower. Histological analysis revealed large differences between the ovaries of superovulat ed and cyclic rats, especially with regard to the maturing follicles. The majority of PMSG/hCG-derived follicles showed hypertrophied theca interna and degenerated or luteinized granulosa. A large number of pre ovulatory follicles did not ovulate. These results clearly indicate th at PMSG/hCG induced follicles are not equal to the follicles developin g during a normal oestrous cycle. This should be taken into considerat ion when using superovulated animals in experiments.