Mechanisms of hydroxyl radical-induced contraction of rat aorta

The present study was designed to investigate the effects of hydroxyl radicals ((OH)-O-.), generated via the Fe2+-mediated Fenton reaction, on isolated rat aortic rings with and without endothelium. In the absence of any vasoactive agent, generation of (OH)-O-. alone elicited an endothelium-independent contraction in rat aortic rings in a concentration-dependent manner. Hydroxyl radical-induced contractions of denuded rat aortic rings appeared, however, to be slightly stronger than those on intact rat aortic rings. The contractile responses to (OH)-O-. were neither reversible nor reproducible in the same ring; even small concentrations of (OH)-O-. radicals resulted in tachyphylaxis. Removal of extracellular calcium ions (Ca2+) or buffering intracellular Ca2+ with 10 muM acetyl methyl ester of bis(o-aminophenoxy) ethane-N,N,N,N,-tetraacetic acid (BAPTA-AM) significantly attenuated the contractile actions of (OH)-O-. radicals. The presence of 1 muM staurosporine, 1 muM bisindolylmaleimide I, 1 muM Go6976 [inhibitor of protein kinase C (PKC)], 2 muM PD-980592 (inhibitor of ERK), 10 muM genistein, and 1 muM wortmannin significantly inhibited the contractions induced by - OH. Proadifen (10 muM), on the other hand, significantly potentiated the hydroxyl radical-induced contractions. Exposure of primary cultured aortic smooth muscle cells to - OH produced significant, rapid rises of intracellular free Ca2+ ([Ca2+](i)). Several, specific antagonists of possible endogenously formed vasoconstrictors did not inhibit or attenuate either hydroxyl radical-induced contractions or the elevation of [Ca2+](i). Our new results suggest that hydroxyl radical-triggered contractions on rat aortic rings are Ca2+-dependent. Several intracellular signal transduction systems seem to play some role in hydroxyl radical-induced vasoconstriction of rat aortic rings. (C) 2004 Elsevier B.V. All rights reserved.