title: Direct effects of estradiol-17 beta on the number of gonadotropin-releasing hormone receptors in the ovine pituitary.
abstract: Concentrations of pituitary receptors for gonadotropin-releasing hormone (GnRH) are affected by GnRH and gonadal steroids. To test the hypothesis that estradiol-17 beta (E2) directly affects the number of GnRH receptors in the pituitary, independent of GnRH secretion, ovariectomized ewes with hypothalamic-pituitary disconnections (HPD) were given 25 micrograms (i.m.) of E2 (HPD + E2, n = 5) or oil (HPD + OIL, n = 5). Ovariectomized control ewes, with intact hypothalamic-pituitary axes (INT), also received either E2 or oil (INT + E2, n = 6; INT + OIL, n = 6). Blood samples were taken hourly for analysis of serum concentrations of luteinizing hormone (LH) from 4 h prior to until 16 h after treatment. Pituitaries were collected 16 h after treatment for analysis of GnRH receptors. Treatment with E2 increased concentrations of LH in serum beginning 12.7 +/- 0.6 h after injection in INT ewes but not in HPD ewes. Compared to INT + OIL ewes, E2 treatment increased (p less than 0.001) the number of GnRH receptors by 2.5-fold in INT ewes and by 2.0-fold in HPD ewes. These results suggest that although GnRH is necessary for secretion of gonadotropins, E2 alone can directly increase the number of GnRH receptors in the pituitary.
authors.affiliation: Department of Physiology, Colorado State University, Fort Collins 80523.
authors.forename: D W
authors.initials: DW
authors.lastname: Gregg
authors.forename: T M
authors.initials: TM
authors.lastname: Nett
mesh_terms: D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D007031:Hypothalamus / Q000502:physiology; D066298:In Vitro Techniques; D007986:Luteinizing Hormone / Q000097:blood; D010052:Ovariectomy; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D011974:Receptors, LH / Q000032:analysis / Q000187:drug effects*; D011966:Receptors, LHRH / Q000187:drug effects* / Q000378:metabolism; D012756:Sheep
chemical_list: D011974:Receptors, LH; D011966:Receptors, LHRH; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone