Circulatory effects of oxygen radicals.

Oxygen radicals have vasoactive properties. The hypoxanthine-xanthine oxidase system generates oxygen radicals. This system relaxes isolated constricted ductus rings from fetal lambs and constricts the pulmonary circulation of adult pigs. Since catalase, and not superoxide dismutase, inhibits the effect of the hypoxanthine-xanthine oxidase system, we believe the effect is caused by the hydroxyl radical. The hydroxyl radical stimulates prostaglandin synthesis in the vessel wall and high concentrations of prostanoids can be measured after hypoxanthine-xanthine oxidase exposure. Indomethacin inhibits the vasoactive effects of the hypoxanthine-xanthine oxidase system. We believe the hypoxanthine-xanthine oxidase system plays an important role in regulating the normal circulation.