title: Melatonin mediates two distinct responses in vascular smooth muscle.
abstract: The pineal hormone melatonin was found to produce two distinct contractile responses in vascular smooth muscle. In isolated rat caudal artery segments, denuded of endothelium, melatonin (10(-10)-10(-7) M) potentiated phenylephrine-induced contractions in a concentration-dependent manner. At higher melatonin concentrations (10(-7)-10(-5) M), however, the potentiating effect was attenuated. In the presence of the melatonin MT2 receptor antagonist, 4-phenyl-2-acetamidotetraline (4P-ADOT), the attenuated constrictor responses were selectively enhanced. These results are consistent with the hypothesis that melatonin activates two receptor subtypes in vascular smooth muscle; MT2 receptors may induce relaxation, while a second receptor subtype mediates vasoconstriction.
authors.affiliation: Department of Pharmacology, College of Medicine, University of California, Irvine 92697-4625, USA.
authors.forename: S
authors.initials: S
authors.lastname: Doolen
authors.forename: D N
authors.initials: DN
authors.lastname: Krause
authors.forename: M L
authors.initials: ML
authors.lastname: Dubocovich
authors.forename: S P
authors.initials: SP
authors.lastname: Duckles
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D004357:Drug Synergism; D066298:In Vitro Techniques; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism; D044094:Receptors, Melatonin; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: C112803:4-phenyl-2-acetamidotetralin; D000316:Adrenergic alpha-Agonists; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D013764:Tetrahydronaphthalenes; D010656:Phenylephrine; D008550:Melatonin