ENDOTHELIUM-DEPENDENT CONTRACTIONS TO OXYGEN-DERIVED FREE-RADICALS IN THE CANINE BASILAR ARTERY

Experiments were designed to determine the effect of oxygen-derived free radicals in isolated canine basilar arteries. Rings with and without endothelium were suspended for isometric tension recording in modified Krebs-Ringer bicarbonate solution bubbled with 95% O2-5% CO2 (temperature = 37-degrees-C; pH = 7.4). A radioimmunoassay technique was used to measure production of prostaglandins and thromboxane B2. Xanthine oxidase (1-9 mU/ml, in the presence of 10(-4) M xanthine) and hydrogen peroxide (10(-6) to 10(-4) M) caused concentration-dependent contractions. The removal of endothelium reversed these contractions into relaxations. Contractions to xanthine oxidase and hydrogen peroxide were inhibited in the presence of superoxide dismutase (150 U/ml), catalase (1,200 U/ml), indomethacin (10(-5) M), and SQ 29548 (10(-6) M) but not in the presence of deferoxamine (10(-4) to 10(-3) M) and dimethyl sulfoxide (10(-4) M). N(G)-monomethyl-L-arginine (3 x 10(-5) M) augmented the contractions to hydrogen peroxide. Xanthine oxidase stimulated production of 6-keto-prostaglandin F1alpha, prostaglandin F2alpha, prostaglandin E2, and thromboxane B2. The stimulatory effect was prevented by the removal of endothelial cells. These studies suggest that xanthine oxidase causes endothelium-dependent contractions mediated by 1) hydrogen peroxide-induced stimulation of the endothelial metabolism of arachidonic acid via the cyclooxygenase pathway, leading to activation of prostaglandin H-2-thromboxane A2 receptors, and 2) inactivation of basal production of nitric oxide by superoxide anions.