title: Modulation of gonadotropin-releasing hormone receptor concentration in cultured female rat pituitary cells by estradiol treatment.
abstract: Short-term (0.5-4 h) treatment of rat pituitary cells in culture with estradiol (E2) results in a significant decrease of Gonadotropin-Releasing Hormone (GnRH) induced LH-release. We studied whether changes in the concentrations of GnRH-receptors (GnRH-R) might account for this phenomenon: pituitary cells from adult female rats were incubated for 4 or 24 h in the presence or absence of 10(-9) M E2. Then saturation curves of D-Ala6-des-Gly10-GnRH ethylamide binding were obtained. In addition, binding studies were carried out in cultures incubated for 0.5, 1, 2 or 4 h with or without 10(-9) M E2 using a near saturating concentration of GnRH-analog. No changes of GnRH-R affinity occurred (4 h experiments: Ka in vehicle treated cells: 0.94 +/- 0.2 x 10(9) M-1, Ka in E2 treated cells: 1.06 +/- 0.3 x 10(9) M-1; 24 h experiments: Ka vehicle: 0.95 +/- 0.2 x 10(9) M-1, Ka E2: 0.82 +/- 0.3 x 10(9) M-1). The GnRH-R concentrations, however, were significantly reduced (44 +/- 3%; P less than 0.001) by 4 h E2 treatment and increased (by 68 +/- 8%; P less than 0.01) by 24 h of E2 treatment. The GnRH induced LH-release in aliquots of the same cell preparations was significantly reduced after 4 h and markedly increased after 24 h of E2 treatment. The experiments on the time-course of the reduction of D-Ala6-GnRH-binding by E2 treatment showed that the number of GnRH-R was significantly decreased (24 +/- 1%; P less than 0.05) already after 0.5 h of exposure to the estrogen. This is also the time period after which the negative E2-effect on GnRH-induced LH-release becomes significant. These data provide first evidence that the short-term negative E2-effect on GnRH induced LH-release by rat pituitary cells in culture could be mediated via a reduction of available GnRH-R.
authors.affiliation: Department of Obstetrics and Gynecology, Medical University of Lübeck, F.R.G.
authors.forename: G
authors.initials: G
authors.lastname: Emons
authors.forename: H G
authors.initials: HG
authors.lastname: Hoffmann
authors.forename: C
authors.initials: C
authors.lastname: Brack
authors.forename: O
authors.initials: O
authors.lastname: Ortmann
authors.forename: R
authors.initials: R
authors.lastname: Sturm
authors.forename: P
authors.initials: P
authors.lastname: Ball
authors.forename: R
authors.initials: R
authors.lastname: Knuppen
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D010902:Pituitary Gland / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011966:Receptors, LHRH / Q000378:metabolism*
chemical_list: D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; C050812:LHRH, Ala(6)-; C010661:surfagon