title: Effects of melatonin in vivo upon luteinizing hormone and prolactin releases induced by opiate receptor antagonists in adult male rats.
abstract: The effects of melatonin on LH and PRL releases induced by treatment with naloxone, naloxone methyliodide and nalmefene were studied in adult male rats. Subcutaneous melatonin injection (1.4 mg/Kg) had no effect on LH secretion, but caused an inhibition effect (84%) on LH release induced by naloxone (2.4 mg/Kg). Melatonin too totally inhibited LH secretion induced by naloxone methyliodide (2.8 mg/Kg) and nalmefene (2 mg/Kg) when it was simultaneously administered with each opioid receptor antagonist. Melatonin alone had no significant effect on serum PRL levels, but decreased by 25.5% the inhibitory effect potency of nalmefene on PRL secretion after simultaneous injections. The inhibitory effect potency of naloxone on PRL release increased (16%) when it was administered with melatonin. Simultaneous injection of melatonin with naloxone methyliodide inhibited PRL release (78%) while naloxone methyliodide alone did not modify this secretion. The results obtained with a quaternary opioid antagonist indicate that the opioid receptor type which mediates LH and PRL responses is located respectively outside and inside the blood-brain barrier. Our findings show that opiate antagonists and their quaternary ammonium salts affect secretion of LH and PRL through different mechanisms susceptible to the influence of melatonin.
authors.affiliation: Laboratoire de Physiologie Pharmaceutique, Faculté de Pharmacie, Rennes, France.
authors.forename: V
authors.initials: V
authors.lastname: Shacoori
authors.forename: B
authors.initials: B
authors.lastname: Saïag
authors.forename: V
authors.initials: V
authors.lastname: Lemay
authors.forename: A
authors.initials: A
authors.lastname: Girre
authors.forename: B
authors.initials: B
authors.lastname: Rault
mesh_terms: D000818:Animals; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D011388:Prolactin / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar
chemical_list: D009292:Narcotic Antagonists; D000644:Quaternary Ammonium Compounds; D009270:Naloxone; D009271:Naltrexone; C041269:N-methylnaloxone; D011388:Prolactin; D007986:Luteinizing Hormone; D008550:Melatonin; C038981:nalmefene