title: Mechanisms underlying the hydrogen peroxide-induced, endothelium-independent relaxation of the norepinephrine-contraction in guinea-pig aorta.
abstract: The mechanisms underlying the hydrogen peroxide-induced relaxation of the norepinephrine-contraction were studied by measuring isometric force, myosin light chain (MLC(20)) phosphorylation and cyclic GMP in endothelium-denuded muscle from the guinea-pig aorta. Norepinephrine (5.2+/-1.3 microM) produced a phasic, followed by a tonic contraction. Hydrogen peroxide (10 and 100 microM), glyceryl trinitrate (30 and 300 nM) and 8-bromo cyclic GMP (30 and 100 microM) did not change the basal tone, but reduced the norepinephrine-induced contraction. Phosphorylation of MLC(20) (percentage of phosphorylated to total MLC(20)) was increased 1 min (5.9+/-1.0% vs. 35.9+/-4.9%) and, to a lesser extent, 20 min (3.7+/-1.7% vs. 13.9+/-1.6%) after the addition of norepinephrine. Hydrogen peroxide (100 microM) did not modify basal MLC(20) phosphorylation, but reduced the increase in MLC(20) phosphorylation induced by 1-min exposure to norepinephrine (20.9+/-4.1%). Its effect was abolished by catalase. When the tissue was incubated for 20 min with norepinephrine in the presence of hydrogen peroxide, norepinephrine-induced MLC(20) phosphorylation was not changed (13.6+/-1.5%), as compared to that in the absence of hydrogen peroxide. Hydrogen peroxide relaxed norepinephrine-stimulated aortas in a concentration-dependent fashion with EC(50) values of 5.9+/-0.2 microM. The relaxation was inhibited by soluble guanylate cyclase inhibitors and increased by an inhibitor of cyclic GMP-selective phosphodiesterase. In aorta precontracted with norepinephrine, hydrogen peroxide (100 microM) relaxed the tissue by 89+/-11% and almost doubled tissue concentrations of cyclic GMP, whereas sodium nitroprusside (1 microM) relaxed the tissue by 100% and increased cyclic GMP concentrations 30-fold. It is suggested that the inhibitory effects of hydrogen peroxide on the norepinephrine-induced phasic and sustained contractions are explained by a decrease in MLC(20) phosphorylation and by an alteration in MLC(20) phosphorylation-independent mechanisms, respectively. The effects of hydrogen peroxide were in part mediated by cyclic GMP.
authors.affiliation: Department of Cellular and Molecular Pharmacology, Nagoya City University Graduate School of Medical Sciences, Mizuho-cho, Mizuho-ku, 467-8601, Nagoya, Japan. fujimoto@med-nagoya-cu.ac.jp
authors.forename: Seigo
authors.initials: S
authors.lastname: Fujimoto
authors.forename: Mayumi
authors.initials: M
authors.lastname: Mori
authors.forename: Hiromi
authors.initials: H
authors.lastname: Tsushima
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology*; D006168:Guinea Pigs; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D018994:Myosin Light Chains / Q000378:metabolism; D005996:Nitroglycerin / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011688:Purinones / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D014661:Vasoconstriction / Q000187:drug effects*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D018994:Myosin Light Chains; D010069:Oxadiazoles; D011688:Purinones; D011810:Quinoxalines; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C016276:8-bromocyclic GMP; D006861:Hydrogen Peroxide; D005996:Nitroglycerin; C011145:zaprinast; D006152:Cyclic GMP; D008751:Methylene Blue; D009638:Norepinephrine