Hydrogen peroxide-induced endothelium-dependent

Abstract

In phenylephrine-precontracted rings, H 2O 2 produced an endothelium-dependent relaxation at concentrations of 4.4 × 10 −7 to ∼4.4 × 10 −5 M. Removal of extracellular Ca 2+ ([Ca 2+] 0) markedly attenuated the relaxant effects of H 2O 2. Complete inhibition of the H 2O 2 relaxant action was obtained after buffering intracellular Ca 2+ ([Ca 2+] i) in endothelial cells, with 10 μM acetyl methyl ester of bis (o-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid (BAPTA-AM). These relaxant effects of H 2O 2 were nearly abolished by 15 × 10 −5 M N G-monomethyl-arginine (L-NMMA) or 5 × 10 −5 M N G-nitro-L-arginine (L-NAME) and were attenuated markedly by the presence of either 10 −6 M Fe 2+, 10 −6 M Fe 3+, or 5 × 10 −6 M methylene blue. These inhibitory effects of L-NMMA or L-NAME could be reversed partly by 5 × 10 −5 M L-arginine. These Fe 2+- and Fe 3+-induced inhibitions of H 2O 2-stimulated relaxation were reduced significantly by either 1.0 mM deferoxamine (a Fe 2+ chelator) or 100 μM dimethyl sulfoxide (DMSO). In addition, 17-octadecynoic acid (2.5 μM) or proadifen (10 μM) (both antagonists of cytochrome P450 metabolism of fatty acids) markedly decreased the H 2O 2 relaxant effects. Proadifen (10 μM) produced concentration-dependent impairment of vasorelaxation to acetylcholine. A variety of amine antagonists and a cyclo-oxygenase inhibitor all fail to interfere with or attenuate the H 2O 2-induced relaxations. Our observations suggest that, at suitable pathophysiologic concentrations, H 2O 2 could induce release of an endothelium-derived relaxing factor, probably nitric oxide, from endothelial cells. The H 2O 2 relaxant effects are clearly Ca 2+-dependent and require formation of cyclic guanosine monophosphate (cGMP). These vasorelaxing effects of H 2O 2 appear to be induced by H 2O 2 itself. Hydrogen peroxide may stimulate production of some unknown metabolites metabolized by cytochrome P450–dependent enzymes.