title: Inhibitory effect of pure 31-kilodalton bovine inhibin on gonadotropin-releasing hormone (GnRH)-induced up-regulation of GnRH binding sites in cultured rat anterior pituitary cells.
abstract: Primary cultures of enzymatically dispersed rat anterior pituitary cells were used to examine the effect of pure 31 kilodalton bovine inhibin on GnRH-induced up-regulation of GnRH binding sites. After 2 days in culture, the cells were exposed to stimuli with or without test substances for 10 h, followed by evaluation of GnRH binding sites using iodinated GnRH-A (Buserelin) as tracer. Inhibin suppressed GnRH-induced up-regulation of GnRH binding sites in a dose-dependent manner with an IC50 of 0.13 U/ml (5.5 pM). The inhibin-related peptides transforming growth factor-beta, and Müllerian inhibitory substance had no detectable effect (stimulatory or inhibitory), suggesting that the action is specific to inhibin. In addition, inhibin inhibited the calcium ionophore A23187-induced up-regulation of GnRH binding sites, indicating that this effect of inhibin can occur, at least in part, at a stage subsequent to Ca2+ mobilization. Inhibin did not compete with iodinated GnRH-A for GnRH binding sites. In conclusion, pure 31 kilodalton bovine inhibin suppressed GnRH-induced up-regulation of GnRH binding sites in cultured rat anterior pituitary cells, providing direct evidence that inhibin modulates delayed actions of GnRH.
authors.affiliation: Medical Research Centre, Prince Henry's Hospital Campus, Monash Medical Centre, Melbourne, Victoria, Australia.
authors.forename: Q F
authors.initials: QF
authors.lastname: Wang
authors.forename: P G
authors.initials: PG
authors.lastname: Farnworth
authors.forename: J K
authors.initials: JK
authors.lastname: Findlay
authors.forename: H G
authors.initials: HG
authors.lastname: Burger
mesh_terms: D000818:Animals; D054304:Anti-Mullerian Hormone; D001667:Binding, Competitive; D002064:Buserelin / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006023:Glycoproteins; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006131:Growth Inhibitors; D007265:Inhibins / Q000494:pharmacology*; D008297:Male; D009095:Mullerian Ducts; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011966:Receptors, LHRH / Q000187:drug effects / Q000378:metabolism*; D013735:Testicular Hormones / Q000494:pharmacology; D015291:Transforming Growth Factors / Q000494:pharmacology
chemical_list: D006023:Glycoproteins; D006131:Growth Inhibitors; D011966:Receptors, LHRH; D013735:Testicular Hormones; D007987:Gonadotropin-Releasing Hormone; D000001:Calcimycin; D007265:Inhibins; D015291:Transforming Growth Factors; D054304:Anti-Mullerian Hormone; D002064:Buserelin; D002118:Calcium