LHRH-induced LH and FSH responses in the aged female rat.
LHRH-induced LH and FSH concentrations were measured in 8 to 12-month-old rats which had just begun to exhibit constant vaginal estrus (CE) or prolonged vaginal diestrus (PD) and in young rats on the day of proestrus (PE). All animals were anesthetized with sodium pentobarbital (31 mg/kg). They received (1) i.v. infusion of LHRH (Beckman 100 ng/ml at a rate of 0.5 ml/hr) for 3 hrs or (2) 2 i.v. injections of LHRH (50 ng/100 g body wt) spaced 120 min apart. LHRH stimulation resulted in a comparable gonadotropin response in young rats and old CE rats; however, old PD rats exhibited a markedly attenuated  LH and FSH response to LHRH infusion. These data suggest that pituitary responsiveness to LHRH does not change in 8 to 12-month-old CE rats and therefore does not play a major role in the transition to acyclicity. In contrast, pituitary responsiveness is decreased in old PD rats early during the aging process and therefore may be an important factor in the transition to their acyclic vaginal smear pattern.
D000375:Aging; D000818:Animals; D004031:Diestrus / Q000187:drug effects; D004971:Estrus / Q000187:drug effects; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007031:Hypothalamus / Q000502:physiology; D007986:Luteinizing Hormone / Q000097:blood*; D010424:Pentobarbital / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D013997:Time Factors
D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D010424:Pentobarbital