Naloxone stimulation of in vivo LHRH release is not diminished following ovariectomy.
The effects of an opiate receptor antagonist, naloxone, on the in vivo release of luteinizing hormone releasing hormone (LHRH) in ovariectomized and intact female rats were examined using push-pull perfusion. Hypothalamic LHRH release rates were determined before and after naloxone (2.5 mg/kg s.c.) or saline vehicle injection in rats during metestrus or 4 or 8 days following ovariectomy. Naloxone was found to be equally effective in significantly (p less than 0.05) stimulating LHRH release in all three treatment conditions. In animals that were fitted with atrial catheters instead of push-pull cannulae, naloxone administration led to significant increases in peripheral LH levels in metestrous and ovariectomized rats. Peripheral follicle-stimulating hormone levels were unaffected by naloxone. These results suggest that opioid inhibitory tone is not diminished during pituitary escape from ovarian negative feedback in adult female rats. Our findings are not consistent with the hypothesis that ovarian negative feedback regulation of LH secretion is serially mediated by endogenous opioid peptide neurons in these animals. Rather, it is proposed that opioid inhibition of LHRH release and ovarian negative feedback may operate in parallel to control LH secretion in the female rat.
D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology*; D010052:Ovariectomy; D010477:Perfusion; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical
D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone