Oxygen-elicited responses in calf coronary arteries: Role of H2O2 production via NADH-derived superoxide

Our previous studies in isolated endothelium-removed calf pulmonary arteries suggest that Po-2-elicited responses are primarily mediated through modulation of guanosine 3',5'-cyclic monophosphate via changes in the generation of H2O2 Originating from superoxide anion (O-2(-).) produced by NADH oxidase activity. In the present study we examined the importance of this mechanism in Po-2-elicited responses of endothelium-removed calf coronary arteries. NADH oxidase activity was found to be the major source of O-2(-). in the homogenate of endothelium-removed calf coronary arteries detected by lucigenin-elicited chemiluminescence. Precontracted endothelium-removed calf coronary arteries show a relaxation to hypoxia, and reoxygenation causes a transient additional relaxation before the recovery of normoxic levels of force. Under these conditions the detection of O-2(-). was decreased by hypoxia and a transient overproduction was observed during reoxygenation. The relaxation to reoxygenation, but not to hypoxia, was significantly inhibited by a scavenger of O-2(-). that prevents the formation of H2O2 (nitro blue tetrazolium), an inhibitor of NAD(P)H oxidases and other O-2(-).-generating flavoproteins (diphenyliodonium), and inhibition of the stimulation of soluble guanylate cyclase (LY-83583). A scavenger of O-2(-). that promotes H2O2 formation (Tiron) did not inhibit the Pop-elicited responses examined. Hypoxia and diphenyliodonium (but not Tiron) decreased the metabolism of endogenous H2O2 by catalase las measured by the H2O2-dependent co-oxidation of methanol to formaldehyde by catalase), and reoxygenation caused a stimulation of H2O2 metabolism by catalase. The presence of endothelium resulted in minor modifications of the Po-2 responses, which were partially mediated via prostaglandins and nitric oxide on the basis of the effects of indomethacin and nitro-L-arginine, respectively These results suggest that in calf coronary arteries the stimulation of guanylate cyclase via H2O2 Originating from NADH-derived O-2(-). production contributes to the transient relaxation to posthypoxic reoxygenation, but not the response to hypoxia.