Hydrogen peroxide-induced endothelium-dependent relaxation of rat aorta - Involvement of Ca2+ and other cellular metabolites

In phenylephrine-precontracted rings, H2O2 produced an endothelium-dependen t relaxation at concentrations of 4.4 x 10(-7\) to similar to 4.4 x 10(-5) M. Removal of extracellular Ca2+ ([Ca2+](0)) markedly attenuated the relaxa nt effects of H2O2. Complete inhibition of the H2O2 relaxant action was obt ained after buffering intracellular Ca2+ ([Ca2+](i)) in endothelial cells, with 10 mM acetyl methyl ester of bis (o-aminophenoxy) ethane-N,N,N',N'-tet raacetic acid (BAPTA-AM). These relaxant effects of H2O2 were nearly abolis hed by 15 X 10(-5) M N-G-monomethyl-arginine (L-NMMA) or 5 x 10(-5) M NG-ni tro-L-arginine (L-NAME) and were attenuated markedly by the presence of eit her 10(-6) M Fe2+, 10(-6) M Fe3+, or 5 x 10(-6) M methylene blue. These inh ibitory effects of L-NMMA or L-NAME could be reversed partly by 5 x 10-5 M L-arginine. These Fe2+- and Fe3+-induced inhibitions of H2O2-stimulated rel axation were reduced significantly by either 1.0 mM deferoxamine (a Fe2+ ch elator) or 100 ELM dimethyl sulfoxide (DMSO). In addition, 17-octadecynoic acid (2.5 mu M) or proadifen (10 mu M) (both antagonists of cytochrome P450 metabolism of fatty acids) markedly decreased the H2O2 relaxant effects. P roadifen (10 mu M) produced concentration-dependent impairment of vasorelax ation to acetylcholine, A variety of amine antagonists and a cyclo-oxygenas e inhibitor all fail to interfere with or attenuate the H2O2-induced relaxa tions. Our observations suggest that, at suitable pathophysiologic concentr ations, H2O2 could induce release of an endothelium-derived relaxing factor , probably nitric oxide, from endothelial cells. The H2O2 relaxant effects are clearly Ca2+ dependent and require formation of cyclic guanosine monoph osphate (cGMP). These vasorelaxing effects of H2O2 appear to be induced by H2O2 itself. Hydrogen peroxide may stimulate production of some unknown met abolites metabolized by cytochrome P450-dependent enzymes. (C) 1999 Elsevie r Science Inc. All rights reserved.