AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 4 663-R669, Copyright © 1986 by American Physiological Society
Environment and hamster reproduction: responses to phase-specific starvation during estrous cycle
L. P. Morin
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.
