NITRIC-OXIDE REGULATES OXYGEN-UPTAKE AND HYDROGEN-PEROXIDE RELEASE BYTHE ISOLATED BEATING RAT-HEART

Isolated rat heart perfused with 1.5-7.5 mu M NO solutions or bradykin in, which activates endothelial NO synthase, showed a dose-dependent d ecrease in myocardial O-2 uptake from 3.2 +/- 0.3 to 1.6 +/- 0.1 (7.5 mu M NO, n = 18, P < 0.05) and to 1.2 +/- 0.1 mu M O-2 . min(-1). g ti ssue(-1)(10 mu M bradykinin, n = 10, P < 0.05). Perfused NO concentrat ions correlated with an induced release of hydrogen peroxide (H2O2) in the effluent (r = 0.99, P < 0.01). NO markedly decreased the O-2 upta ke of isolated rat heart mitochondria (50% inhibition at 0.4 mu M NO, r = 0.99, P < 0.001). Cytochrome spectra in NO-treated submitochondria l particles showed a double inhibition of electron transfer at cytochr ome oxidase and between cytochrome b and cytochrome c, which accounts for the effects in Oa uptake and H2O2 release. Most NO was bound to my oglobin; this fact is consistent with NO steady-state concentrations o f 0.1-0.3 mu M, which affect mitochondria. In the intact heart, finely adjusted NO concentrations regulate mitochondrial O-2 uptake and supe roxide anion production (reflected by H2O2), which in turn contributes to the physiological clearance of NO through peroxynitrite formation.