title: Gonadotropin releasing hormone inhibitory autofeedback by subproducts antagonist at N-methyl-D-aspartate receptors: a model of autocrine regulation of peptide secretion.
abstract: The secretion of Gonadotropin-releasing Hormone (GnRH) involves activation of N-methyl-D-aspartate (NMDA) receptors. Here, we show that pulsatile GnRH secretion from hypothalamic explants is suppressed by 1-5GnRH, an endogenous breakdown product of GnRH, while 2-10GnRH has no effect. GnRH secretion evoked by NMDA is selectively inhibited by 1-5GnRH and this effect is similar to that of AP-5, a competitive antagonist at NMDA receptors. In addition, 1-5GnRH accounts for a dose-related inhibition of tritiated glutamate binding to hypothalamic membrane preparations. Using GnRH secretion as a model of NMDA-receptor controlled system, the effect of different peptides has been studied. Growth Hormone Releasing Factor (GRF), Insulin-like Growth Factor-I (IGF-I) and Proinsulin result in inhibition of GnRH secretion. Bioactive subproducts of those peptides (1-29GRF, 4-701GF-I and insulin) do not show any effect, suggesting that their classical receptors are not involved. In contrast, GnRH secretion is inhibited by other subproducts (1-37GRF, 1-31GF-I and C-peptide) all terminating in a glutamate residue. These subproducts selectively suppress the NMDA-evoked secretion of GnRH. Protease inhibitors prevent the inhibitory effects of IGF-I on GnRH secretion. This, breakdown products of different peptide hormones are possible endogenous antagonists at NMDA receptors. This effect could account for an autocrine or paracrine limitation of NMDA-receptor-mediated secretion of peptides.
authors.affiliation: Department of Pediatrics, University of Liège, C.H.U. Sart Tilman, Belgium.
authors.forename: J P
authors.initials: JP
authors.lastname: Bourguignon
authors.forename: M L
authors.initials: ML
authors.lastname: Alvarez Gonzalez
authors.forename: A
authors.initials: A
authors.lastname: Gerard
authors.forename: P
authors.initials: P
authors.lastname: Franchimont
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005246:Feedback; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism* / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000502:physiology
chemical_list: D010446:Peptide Fragments; D016194:Receptors, N-Methyl-D-Aspartate; D007987:Gonadotropin-Releasing Hormone; D007334:Insulin-Like Growth Factor I; D013007:Growth Hormone-Releasing Hormone