title: Suppression in gonadotropes of gonadotropin-releasing hormone-stimulated follicle-stimulating hormone release by the gonadal- and neurosteroid 3 alpha-hydroxy-4-pregnen-20-one involves cytosolic calcium.
abstract: The gonadal- and neurosteroid 3 alpha-hydroxy-4-pregnen-20-one (3 alpha HP) suppresses FSH release in cultures of anterior pituitary cells. In a previous report, we showed that this suppression is achieved at least in part by an interaction at the plasma membrane level. We undertook to examine the possible interaction of 3 alpha HP at the level of intracellular Ca2+. Anterior pituitary cells from adult randomly cycling female rats were treated for 4 h with 10 nM GnRH and 0.1 nM 3 alpha HP with or without protein kinase C activator (SC10), antagonist (H-7), intracellular Ca2+ chelator (TMB-8), and intracellular Ca2+ mobilizer (glutamate), and with or without EGTA and Ca2+ in the medium. FSH content in media and cells was determined by RIA. The protein kinase C (PKC) activator, SC10, increased basal levels of secreted FSH. 3 alpha HP suppressed (P < 0.05) SC10-stimulated basal FSH release. The PKC inhibitor, H7, decreased GnRH-induced FSH release; FSH was further suppressed (P < 0.05) by 3 alpha HP in the presence of H7. These results were interpreted to indicate that 3 alpha HP may act in part at the level of PKC and also at another site(s). The intracellular Ca2+ chelator, TMB-8, suppressed released and cellular GnRH-stimulated FSH to the same extent as 3 alpha HP; FSH was not further decreased by 3 alpha HP in the presence of TMB-8. 3 alpha HP suppressed glutamate-stimulated FSH release in Ca(2+)-free medium (P < 0.01). Moreover, GnRH-induced release of FSH was suppressed to the same degree by 10(-10) M 3 alpha HP as by 10(-4) M EGTA. In pituitary cell suspensions, the GnRH-induced [Ca2+]i elevations were significantly (P < 0.05) attenuated by 3 alpha HP. From these and previous results, a model is proposed for the action of 3 alpha HP. The model suggests that 3 alpha HP may interact with gonadotropes at the level of the PKC cell signaling pathway and intracellular Ca2+ mobilization, in addition to the plasma membrane/calcium channel. The interaction effects a decrease in intracellular Ca2+, leading to decreases in FSH release from those pituitary gonadotropes that are responsible for FSH. The consistent decrease in total FSH (released plus cellular content) by 3 alpha HP suggests that this neurosteroid may also suppress FSH synthesis.
authors.affiliation: Hormonal Regulatory Mechanisms Laboratory, University of Western Ontario, London, Canada.
authors.forename: J P
authors.initials: JP
authors.lastname: Wiebe
authors.forename: S
authors.initials: S
authors.lastname: Dhanvantari
authors.forename: P H
authors.initials: PH
authors.lastname: Watson
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
mesh_terms: D004092:20-alpha-Dihydroprogesterone / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D005640:Follicle Stimulating Hormone / Q000037:antagonists & inhibitors*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D004092:20-alpha-Dihydroprogesterone; C052610:3-hydroxypregn-4-en-20-one; D007987:Gonadotropin-Releasing Hormone; D005640:Follicle Stimulating Hormone; D011493:Protein Kinase C; D002118:Calcium