POTENTIAL ROLE OF NADH OXIDOREDUCTASE-DERIVED REACTIVE O-2 SPECIES IN CALF PULMONARY ARTERIAL PO-2-ELICITED RESPONSES

Our laboratory tory has previously reported evidence that tone responses of isolated endothelium-removed calf pulmonary arteries elicited by changes in Po-2 appear to be mediated via changes in H2O2 and guanosine 3',5'-cyclic monophosphate, and that the Po-2 sensor mechanism is hypothesized to involve changes in superoxide anion (O-2(-).) production by a microsomal NADH- oxidoreductase, which is the major source of O-2(-). detected by lucigenin-elicited chemiluminescence (CL) in this tissue. In this study we examined if the flavoprotein-directed inhibitor of O-2(-). producing NAD(P)H oxidoreductases, diphenyliodonium (DPI), could be employed as an inhibitor of O; production by NADH oxidoreductase, which functions as a selective probe for PO2-elicited tone responses in calf pulmonary arterial smooth muscle. It was found that 1 mu M DPI inhibited NADH dependent production of CL in the arterial smooth muscle homogenate by 49% (n = 10). DPI reduced basal CL from endothelium-removed pulmonary arteries by 41% (n = 15). In endothelium-removed pulmonary arteries precontracted with U-46619, the hypoxic contraction of 2.3 +/- 0.5 g was reduced to 0.1 +/- 0.4 g (n = 7) by DPI, and the reoxygenation relaxation of 32.7 +/- 7.5% was decreased to 4.4 +/- 1.4% (n = 7). DPI did not have any significant effect on U-46619- or K+-elicited tone generation. DPI also did not alter the relaxation to H2O2 (1 mu M-0.1 mM, n = 6), nitric oxide (0.42 nM-420 nM, n = 12), or isoproterenol (1 nM-1 mu M, n = 6). Probes for other flavoprotein O-2(-). -producing systems, including xanthine oxidase (0.1 mM oxypurinol), nitric oxide synthase (0.1 mM nitro-L-arginine), or mitochondrial electron transport (50 mu M rotenone) did not alter the tone response to changes in PO2. These results are consistent with a hypothesized role for H2O2 formation via NADH oxidoreductase-derived O-2(-). in pulmonary artery responses to changes in PO2.