Postovariectomy decline in the in vitro release of LH-releasing hormone is not manifested in aging female rats.

Aging of the female reproductive system is associated with a transition from a regular cyclic to an irregular cyclic and finally to an acyclic mode of function. We addressed the question: is the transition associated with a decline in the secretory response of the LHRH neuron to an external stimulus and with a change in steroid regulation of the secretory function of the LHRH neuron? Three groups of virgin female rats ranging from 2 to 7 months of age were used: intact, ovariectomized (8 days) and ovariectomized treated with estradiol-17 beta for 49-50 h; explants of the median eminence area (MEA) were incubated in vitro and LHRH release in response to the combined actions of copper and prostaglandin E2 was used as a criterion for secretory function. Based on vaginal cytology, young (2-3 months) females exhibited regular estrous cycles, the transition to irregular cycles manifested at 5 months of age (2/3 of animals) and to acyclicity at 7 months (all animals). In intact animals, there was a doubling in the magnitude of basal as well as stimulated LHRH release which paralleled the increase in MEA content of the peptide. By comparison to intact, stimulated LHRH release was markedly (greater than or equal to 50%; p less than 0.001) attenuated in 2- and 3-month-old ovariectomized rats but not in 5- and 7-month-old rats; thus, stimulated LHRH release at 5-7 months was approximately 2.5-fold greater than at 2-3 months of age. At each age group, estradiol treatment did not alter the magnitude of stimulated LHRH release. Ovariectomy with or without estradiol did not alter basal release nor the MEA content of LHRH.(ABSTRACT TRUNCATED AT 250 WORDS)