Endothelium-dependent contractions to oxygen-derived free radicals in the canine basilar artery

Abstract

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% O 2-5% CO 2 (temperature = 37°C: pH = 7.4). A radioimmunoassay technique was used to measure production of prostaglandins and thromboxane B 2. 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 F(1α), prostaglandin F(2α), prostaglandin E 2, and thromboxane B 2. 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 A 2 receptors, and 2) inactivation of basal production of nitric oxide by superoxide anions.