title: Melatonin exerts its analgesic actions not by binding to opioid receptor subtypes but by increasing the release of beta-endorphin an endogenous opioid.
abstract: The occurrence of systematic diurnal variations in pain thresholds has been demonstrated in human. Salivary melatonin levels change following acute pain when other factors that could explain the change have been removed or controlled. Melatonin-induced analgesia is blocked by naloxone or pinealectomy. By using selective radioligands [3H]-DAMGO, [3H]-DPDPE, [3-U69593, and 3H]-nociceptin, we have shown that the bovine pinealocytes contain delta and mu, but not kappa or ORL1 opioid receptor subtypes. In the present study, by using melatonin receptor agonists (6-chloromelatonin or 2-iodo-N-butanoyl-5-methoxytryptamine) or melatonin receptor antagonist (2-phenylmelatonin), we have shown that these agents do not compete with opioid receptor subtypes. However, we observed a time-dependent release of beta-endorphin an endogenous opioid peptide, by melatonin from mouse pituitary cells in culture. Hence, it is suggested that melatonin exerts its analgesic actions not by binding to opioid receptor subtypes but by binding to its own receptors and increasing the release of beta-endorphin.
authors.affiliation: Department of Pathology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58203, USA.
authors.forename: Shaik
authors.initials: S
authors.lastname: Shavali
authors.forename: Begonia
authors.initials: B
authors.lastname: Ho
authors.forename: Piyarat
authors.initials: P
authors.lastname: Govitrapong
authors.forename: Saiphon
authors.initials: S
authors.lastname: Sawlom
authors.forename: Amornpan
authors.initials: A
authors.lastname: Ajjimaporn
authors.forename: Sirirat
authors.initials: S
authors.lastname: Klongpanichapak
authors.forename: Manuchair
authors.initials: M
authors.lastname: Ebadi
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000493:pharmacokinetics; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000493:pharmacokinetics; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000493:pharmacokinetics; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D008550:Melatonin / Q000819:agonists / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000494:pharmacology*; D051379:Mice; D009270:Naloxone / Q000737:chemistry / Q000494:pharmacology; D018847:Opioid Peptides / Q000493:pharmacokinetics; D010870:Pineal Gland / Q000166:cytology* / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid / Q000819:agonists / Q000145:classification / Q000378:metabolism*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D014316:Tritium / Q000493:pharmacokinetics; D001615:beta-Endorphin / Q000378:metabolism*; D000097629:Nociceptin
chemical_list: D000700:Analgesics; D000701:Analgesics, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D008550:Melatonin; D009270:Naloxone; D018847:Opioid Peptides; D011957:Receptors, Opioid; D014316:Tritium; D001615:beta-Endorphin; D000097629:Nociceptin; C100536:2-phenylmelatonin; C085309:N-butanoyl-5-methoxytryptamine; C024100:6-chloromelatonin