NITROGEN-DIOXIDE CAUSES PULMONARY ARTERIAL RELAXATION VIA THIOL NITROSATION AND NO FORMATION

Micromolar concentrations of nitrogen dioxide (NO2), a key metabolite of nitric oxide (NO) and peroxynitrite (ONOO-) were observed to cause a prolonged relaxation of isolated endothelium-removed rings of bovine pulmonary arteries (BPA) precontracted with 30 mM potassium. Relaxati on to NO2 was markedly inhibited by 1 mu M hemoglobin (Hb), 10 mu M me thylene blue (MB), and 10 mu M LY-83583, The response to NO2 was enhan ced in the presence of 1 mM reduced glutathione (GSH) or cysteine. The addition of NO2 to Krebs bicarbonate buffer (under 95% N-2-5% CO2) co ntaining 1 mM GSH or BPA resulted in an increase in NO formation (meas ured in head space gas). Relaxation to NO2, and NO formation were mark edly decreased after GSH depletion by pretreatment of BPA with diethyl maleate. A high-performance liquid chromatography analysis of the pro ducts formed immediately after the addition of NO2 to GSH detected a p reviously isolated (but not identified) potent relaxing agent formed b y a reaction of GSH with ONOO-, and this material comigrated with a sy nthetic product thought to be S-nitro-GSH (GSNO(2)). Nanomolar concent rations of GSNO(2) caused a potent dose-dependent relaxation that was inhibited by Hb, MB, and LY-83583. Therefore NO2 appears to cause a pr olonged guanosine 3',5'-cyclic monophosphate-mediated relaxation in BP A via thiol nitration and a subsequent time-dependent release of NO. T hus NO2 (and ONOO-) may function in a tissue hormonelike regulatory ro le in inflammatory processes in which large amounts of these species a re produced.