Environment and hamster reproduction: responses to phase-specific starvation during estrous cycle.

Reproductive capacity of female hamsters, as estimated by the ovulatory response, is particularly susceptible to interference by food deprivation. Previous studies showed that hamsters generally fail to ovulate if deprived of food for one or two estrous cycles. The present work demonstrates that starvation which is specific to the 2 days immediately after ovulation will block the next expected ovulation in approximately 80% of the animals. Such phasic starvation also resulted in significantly smaller ovarian follicle sizes. When placed with vigorous males, anovulatory animals failed to show lordosis behavior unless exogenous estradiol benzoate (EB) was supplied. With EB provided, all animals showed short-latency lordosis. These bioassay data suggested that poorly developed follicles were secreting insufficient estradiol for the facilitation of lordosis. Exogenous luteinizing hormone (LH) given 6 h before lights off on cycle day 4 failed to elicit ovulation, further suggesting that the follicles were not mature. Radioimmunoassay of LH and follicle-stimulating hormone (FSH) levels during the ovulatory gonadotropin surge showed that LH was vastly reduced, whereas FSH was in the low-to-normal range. Estradiol levels, assayed immediately before the gonadotropin surge, were low compared with controls, whereas progesterone levels were higher than normal. The results suggest that ovulatory failure in response to phasic food deprivation is a joint function of absence of an ovulatory LH surge and a set of immature follicles.