Mechanisms of hydroxyl radical-induced contraction of rat aorta

Abstract

The present study was designed to investigate the effects of hydroxyl radicals ( OH), generated via the Fe 2+-mediated Fenton reaction, on isolated rat aortic rings with and without endothelium. In the absence of any vasoactive agent, generation of OH 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 were neither reversible nor reproducible in the same ring; even small concentrations of OH radicals resulted in tachyphylaxis. Removal of extracellular calcium ions (Ca 2+) or buffering intracellular Ca 2+ with 10 μM acetyl methyl ester of bis( o-aminophenoxy) ethane- N, N, N′, N′,-tetraacetic acid (BAPTA-AM) significantly attenuated the contractile actions of OH radicals. The presence of 1 μM staurosporine, 1 μM bisindolylmaleimide I, 1 μM Gö6976 [inhibitor of protein kinase C (PKC)], 2 μM PD-980592 (inhibitor of ERK), 10 μM genistein, and 1 μM wortmannin significantly inhibited the contractions induced by OH. Proadifen (10 μM), 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 Ca 2+ ([Ca 2+] i). Several, specific antagonists of possible endogenously formed vasoconstrictors did not inhibit or attenuate either hydroxyl radical-induced contractions or the elevation of [Ca 2+] i. Our new results suggest that hydroxyl radical-triggered contractions on rat aortic rings are Ca 2+-dependent. Several intracellular signal transduction systems seem to play some role in hydroxyl radical-induced vasoconstriction of rat aortic rings.