Superoxide anion inhibits cGMP-associated bovine pulmonary arterial relaxation

We have reported evidence that endothelium-independent relaxations of isolated bovine pulmonary arteries to H2O2 and to reoxygenation with 95% O2-5% CO2 after brief exposure to N2 (5% CO2) appear to be mediated by the activation of guanylate cyclase via H2O2 metabolism through catalase. Treatment of endothelium-removed pulmonary arteries with a potential guanylate cyclase-inhibitor, LY 83583, or with the inhibitor of the Zn+2, Cu+2-superoxide dismutase (SOD) diethyldithiocarbamic acid (DETCA), antagonized guanosine 3',5'-cyclic monophosphate (cGMP)-associated relaxation to H2O2, to reoxygenation and to glyceryl trinitrate, but not the adenosine 3',5'-cyclic monophosphate-associated relaxation to isoproterenol. Superoxide anion (O2-.) levels, detected by lucigenin-elicited chemiluminescence, were enhanced by LY 83583 or DETCA treatment of pulmonary arteries at ambient PO2. Chemiluminescence produced by LY 83583 was markedly potentiated by DETCA treatment, decreased at addition of exogenous SOD, and inhibited markedly by anoxia. LY 83583, but not DETCA, stimulated cyanide-insensitive O2 consumption, consistent with redox cycling of the compound independent of mitochondrial respiration. We propose that O2-. generated on the metabolism of LY 83583, or from cellular electron donors after SOD inhibition by DETCA, inhibits cGMP-mediated relaxations of pulmonary arteries.