title: Effect of melatonin on vascular responses in aortic rings of aging rats.
abstract: In old animals a marked reduction in endothelium-dependent relaxation occurs. Since there is evidence that the endothelial dysfunction associated with aging may be partly related to the local formation of reactive oxygen species, the purpose of this study was to examine the effect of the natural antioxidant melatonin (10(-5)mol/l) on in vitro contractility of aged aortic rings under conditions of increased oxidative stress (40 m mol/l glucose concentration in medium). Experiments were carried out in 18-20 months old, Wistar male rats, using adult (6-7 months old) animals as controls. A higher plasma lipid peroxidation was found in aged rats as compared to the younger ones. In a first experiment, dose-response curves for acetylcholine-induced relaxation of aortic rings were conducted. Analyzed as a main factor in a factorial ANOVA, age decreased and melatonin augmented the relaxing response to acetylcholine. melatonin's restoring effect on aortic ring relaxation was found in aged aortic rings only and was more pronounced in the presence of a high glucose medium. In a second experiment, the effect of melatonin on the contractility response to phenylephrine of intact or endothelium-denuded aortic rings obtained from aged or control rats was examined in normal or high glucose medium. A main factor analysis in the factorial ANOVA indicated that age and operation augmented, and melatonin decreased, aortic ring contractility response to phenylephrine. Melatonin's restoring effect on aortic contractility was seen in aged aortic rings. The effect of age or a high glucose medium on phenylephrine-induced contractility was more pronounced in the absence of an intact endothelium. Aging did not affect the relaxant response of intact or endothelium-denuded rings to sodium nitroprusside. The results support the improvement by melatonin of vascular response in aging rats, presumably via its antioxidant activity.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Buenos Aires, Paraguay 2155, 1121 Buenos Aires, Argentina.
authors.forename: Carlos F
authors.initials: CF
authors.lastname: Reyes-Toso
authors.forename: Daniel
authors.initials: D
authors.lastname: Obaya-Naredo
authors.forename: Conrado R
authors.initials: CR
authors.lastname: Ricci
authors.forename: Fernando M
authors.initials: FM
authors.lastname: Planells
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Pinto
authors.forename: Laura M
authors.initials: LM
authors.lastname: Linares
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Cardinali
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000375:Aging / Q000502:physiology*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D001013:Aorta, Thoracic / Q000187:drug effects*; D001786:Blood Glucose / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009599:Nitroprusside / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D001786:Blood Glucose; D004791:Enzyme Inhibitors; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine; D019001:Nitric Oxide Synthase; D008550:Melatonin; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester