Involvement of nitric oxide and nitrosothiols in relaxation of pulmonary arteries to peroxynitrite.

Peroxynitrite (ONOO-) is an inflammatory cell-derived oxidant, formed by the reaction of superoxide anion (O2-) with nitric oxide (NO), which was recently reported to relax vascular tissues. In the present study, the potential role of NO in the mechanism of relaxation in isolated bovine endothelium-denuded pulmonary arterial smooth muscle rings to ONOO- was evaluated. Potassium-preconstricted pulmonary arterial rings rapidly relaxed for a prolonged period of time on exposure to ONOO- (0.01-0.1 mM). The relaxation after 1 min of exposure to ONOO- (0.1 mM) was reduced 49 and 87%, respectively, by inhibitors of the stimulation of soluble guanylate cyclase, methylene blue, and LY-83583. In contrast, a scavenger of hydroxyl radicals, dimethyl sulfoxide, did not alter this response. Decomposed 0.1 mM ONOO- (which is primarily nitrite) and 0.1 mM nitrite caused a relaxation of pulmonary artery, which slowly developed over 15 min. Small quantities of NO were detected by chemiluminescence quantification methods when ONOO- was added to buffer. Exposure of pulmonary arterial tissue or buffer containing glutathione (GSH) to ONOO- caused a time-dependent increase in the observed generation of NO, whereas decomposed ONOO- produced 10% of the NO generated by ONOO- on incubation with pulmonary arterial tissue. Treatment with diethyl maleate, an agent that depletes tissue GSH, reduced both the relaxation and the formation of NO detected from pulmonary artery on exposure to ONOO-. GSH solutions treated with ONOO- appear to have generated a nitrosothiol-like vascular relaxant compound. Thus ONOO- appears to relax vascular tissue, in part, by nitrosylating tissue GSH (or other thiols), which subsequently releases NO over prolonged time periods.