title: Temporal changes occur in the neuroendocrine control of gonadotropin secretion in aging female rats: role of progesterone.
abstract: The present study examined the gonadotropin surge-inducing actions of estradiol (E(2)), both alone and with progesterone (P(4)), in middle-aged, early persistent-estrous (PE) female rats that had become PE within 35 days. In addition, we also assessed the effect of P(4) on the mating-induced gonadotropin surges in these acyclic animals. Early PE rats were ovariectomized and received E(2) implants (Day 0). On Day 4, an s.c. injection of P(4) (0.5 mg/ 100 g body weight) at 1200 h markedly increased plasma P(4) and elicited both LH and FSH surges, whereas vehicle-treated controls displayed no rise in P(4) or gonadotropins. This observation confirms that at middle age, female rats no longer respond to the positive-feedback stimulation of E(2) on gonadotropin surges whenever the estrous cyclicity ceases. As PE continued, such a surge-inducing action of E(2) plus P(4) became diminished after 75 days of PE and disappeared thereafter. When caged with males, vehicle-treated early PE rats display a mating-induced increase in P(4) from the adrenal along with small gonadotropin surges. The amplitude of these mating-induced gonadotropin surges was enhanced by supplementation with exogenous P(4) in early PE rats. Our findings indicate that during the early phase of PE, the surge-inducing action of E(2) and P(4) remains intact but deteriorates as PE continues. Thus, a deficiency in P(4) secretion during aging may contribute to the diminished gonadotropin surge response in the hypothalamic-pituitary axis and the subsequent cessation of estrous cyclicity.
authors.affiliation: Department of Obstetrics/Gynecology, D. Geffen School of Medicine at University of California, Los Angeles, CA 90095, USA.
authors.forename: Houng-Wei
authors.initials: HW
authors.lastname: Tsai
authors.forename: Philip S
authors.initials: PS
authors.lastname: LaPolt
authors.forename: Angelica P
authors.initials: AP
authors.lastname: Olcott
authors.forename: John K H
authors.initials: JK
authors.lastname: Lu
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D004343:Drug Implants; D004958:Estradiol / Q000097:blood / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood* / Q000378:metabolism; D007986:Luteinizing Hormone / Q000097:blood* / Q000378:metabolism; D008297:Male; D009490:Neurosecretory Systems / Q000187:drug effects* / Q000502:physiology; D010052:Ovariectomy; D011187:Posture; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*; D051381:Rats; D020318:Rats, Long-Evans; D012726:Sexual Behavior, Animal / Q000187:drug effects
chemical_list: D004343:Drug Implants; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone