Antagonist of gonadotropin-releasing hormone blocks naloxone-induced elevations in serum luteinizing hormone.
Administration of a gonadotropin-releasing hormone (GnRH) antagonist, [D-Phe, D-Trp3.6]-GnRH, to immature female rats blocks the equivalent elevations in serum luteinizing hormone (LH) which are provoked by exogenous, natural GnRH (8 ng/100 g BW) or naloxone (0.25 mg/100 g BW), a specific opiate antagonist. A significant inhibition of GnRH- or naloxone-induced release of LH is obtained when rats are pretreated for 0, 15, 30 or 60 min with 5,000 ng/100 g BW of GnRH antagonist but no inhibition is evident when the antagonist is injected 180 min before either stimulant of LH secretion. A similar time-course is observed for GnRH antagonist inhibition of basal LH levels. The minimally effective dose of GnRH antagonist for suppressing both GnRH- and naloxone-induced LH release is 1,000 ng/100 g BW. More than 80% of the LH response to GnRH or naloxone is blocked by the highest tested dose (10,000 ng/100 g BW) of GnRH antagonist. Since naloxone has no direct influence on pituitary release of LH, these similar influences of GnRH antagonist on the LH-releasing properties of natural GnRH and naloxone, strongly suggest that the systemic administration of the opiate antagonist, naloxone, stimulates the release of endogenous GnRH.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood*; D009270:Naloxone / Q000494:pharmacology*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D051381:Rats; D011919:Rats, Inbred Strains
D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; C034511:LHRH, pGlu(1)-Phe(2)-Trp(3,6)-; D007986:Luteinizing Hormone; D011761:Pyrrolidonecarboxylic Acid