Oxygen metabolites and vasodilator mechanisms in rat cremasteric arterioles

The effects of oxygen metabolites (superoxide anion and hydrogen peroxide) on male Wistar rat cremasteric arterioles and the involvement of these species in the mechanism of vasodilation to arachidonic acid and bradykinin were examined by in vivo television microscopy. In the present study, xanthine oxidase-derived oxygen metabolites from endogenous substrates elicited vasodilation that was selectively and almost completely inhibited by catalase but not by superoxide dismutase. These findings implicate hydrogen peroxide as the vasoactive metabolite generated. Topical application of hydrogen peroxide itself on cremasteric arterioles caused concentration-dependent dilation over the range of 10(-7) to 10(-4) M. Responses to hydrogen peroxide concentrations of up to 10(-5) M were completely inhibited by indomethacin, suggesting that hydrogen peroxide-induced increases in vessel diameter are primarily mediated through the production of vasodilator prostaglandins. In this study, we have not found any evidence to suggest that dilator responses to arachidonic acid or bradykinin are mediated through the extracellular generation of oxygen metabolites. Hydrogen peroxide-induced vasodilation might be involved in the events linking the sensing of oxygen tension through intracellular peroxide formation to the production of vasoactive mediators in the cremasteric microcirculation.