NO elicits prolonged relaxation of bovine pulmonary arteries via endogenous peroxynitrite generation

NO elicits prolonged relaxation of bovine pulmonary arteries via endogenous peroxynitrite generation. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L437-L444, 1997.-We previously reported that acute exposure of endothelium-removed bovine pulmonary arteries (BPA) to high levels (0.1 mM) of peroxynitrite (ONOO-) caused a prolonged guanosine 3',5'-cyclic monophosphate-related relaxation that appeared to be mediated through a thiol-dependent generation of nitric oxide (NO). In this study, we examined the importance of endogenous ONOO- formation in the regulation of BPA force generation by elevated physiological levels of NO. Exposure of BPA precontracted with 30 mM KCl to similar to 50 nM NO for 2 min caused a subsequent prolonged relaxation of KCl-induced force and an increased release of NO (measured in head space gas after a 5-min deoxygenation with 95% N-2-5% CO2). This subsequent release of NO was reduced after depletion of tissue glutathione with diethyl maleate (DEM). Also, the NO-elicited prolonged relaxation of BPA was reversed by post-NO treatment with 10 mu M methylene blue (MB; which inhibits guanylate cyclase stimulation by NO) or 1 mu M oxyhemoglobin (which traps NO). Furthermore, inhibiting the biosynthesis of endogenous superoxide anion (O-2(-) .) with 1 mu M diphenyliodonium (DPI) or scavenging O-2(-) . with 10 mM Tiron also promoted reversal of the NO-elicited prolonged relaxation seen in BPA after NO gas exposure. During exposure of BPA smooth muscle to similar to 50 nM NO gas, there appears to be a marked increase in ONOO- formation as detected by a DPI- and Tiron-inhibitable prominent increase in luminol-dependent chemiluminescence and a decrease in O-2(-) . levels as detected by a reduction in lucigenin-dependent chemiluminescence during exposure to NO. Thus, during exposure to elevated physiological levels of NO, BPA appear to produce ONOO-, a species that seems to participate in prolonging the initial relaxation to NO through a thiol-dependent trapping and/or regeneration of NO.