title: [Melatonin influences the release of endogenous opioid peptides in rat periaqueductal gray].
abstract: The present study was undertaken to explore central mechanisms underlying the analgesic effect of melatonin. Push-pull perfusion technique and radioimmunoassay were used to observe the changes in the contents of beta-endorphin (beta-Ep) and leucine-enkephalin (L-EK) in the perfusate from the rat periaqueductal gray (PAG) after administration of melatonin. 30  50 min after an intraperitoneal injection of melatonin (110 mg/kg), the beta-Ep content in the perfusate was increased significantly, while the L-EK content was not changed. Pain threshold was measured using the warm water tail-flick test during the push-pull perfusion of the PAG. It was found that the rat pain threshold was increased significantly 40 min after the intraperitoneal injection of melatonin (110 mg/kg). The results suggest that melatonin may promote the release of beta-Ep in the PAG, which may be one of the mechanisms of the analgesic effect of melatonin.
authors.affiliation: State Key Laboratory of Medical Neurobiology, Department of Neurobiology, Shanghai Medical University, Shanghai 200032, China.
authors.forename: C X
authors.initials: CX
authors.lastname: Yu
authors.forename: G C
authors.initials: GC
authors.lastname: Wu
authors.forename: S F
authors.initials: SF
authors.lastname: Xu
authors.forename: C H
authors.initials: CH
authors.lastname: Chen
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004743:Enkephalin, Leucine / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D017288:Pain Threshold / Q000187:drug effects; D010487:Periaqueductal Gray / Q000378:metabolism*; D011897:Random Allocation; D051381:Rats; D001615:beta-Endorphin / Q000378:metabolism*
chemical_list: D000701:Analgesics, Opioid; D004743:Enkephalin, Leucine; D001615:beta-Endorphin; D008550:Melatonin