Endogenous peroxynitrite generation causes a subsequent suppression of coronary arterial contraction to serotonin

High levels of exogenous peroxynitrite (ONOO-) have been reported to cause coronary vascular relaxation by a mechanism that appears to involve the subsequent generation of nitric oxide (NO). In this study, we examined if endogenous vasoactive levels of ONOO are formed from endogenous superoxide anion (O2-.) upon exposure of isolated endothelium-removed bovine coronary arteries (BCA) to biological levels of NO. During exposure of BCA to approximately 50 nM NO for 2 min, the level of endogenous O2-. detected by lucigenin-dependent chemiluminescence (CL) was markedly decreased and an increase in luminol-dependent CL was observed, consistent with the detection of ONOO generation. NO treatment caused a decrease in contraction of BCA to 0.1-3 microM serotonin (5-HT). This suppression of contraction to 5-HT was completely prevented by preincubation prior to NO exposure with agents that prevent endogenous O2-. production (10 microM diphenyliodonium) or trap intracellular O2-. (10 mM Tiron) or ONOO (0.1 mM urate), and by post-NO treatment with an agent that traps NO (1 microM oxyhemoglobin) or prevents the stimulation of cGMP production by NO (10 microM methylene blue). The NO treatment caused a subsequent release of NO (measured in the head space after a 5-min equilibration with 95% N2-5% CO2), and this subsequent release of NO was reduced by the presence of urate during NO exposure and by depletion of endogenous tissue glutathione (by pretreatment with 7 mM diethyl maleate). Thus, exposure of BCA to elevated physiological levels of NO causes a prolonged suppression of contraction to 5-HT which appears to result from endogenous ONOO formation and a thiol-dependent process that traps and subsequently releases vascular relaxant levels of NO.