Endothelial nitric oxide synthase (NOS3) knockout decreases NOS2 induction, limiting hyperoxygenation and conferring protection in the postischemic heart

Although it has been shown that endothelial nitric oxide synthase ( eNOS)- derived nitric oxide downregulates mitochondrial oxygen consumption during early reperfusion, its effects on inducible NOS ( iNOS) induction and myocardial injury during late reperfusion are unknown. Wild- type ( WT) and eNOS(-/-) mice were subjected to 30 min of coronary ligation followed by reperfusion. Expression of iNOS mRNA and protein levels and peroxynitrite production were lower in postischemic myocardium of eNOS(-/-) mice than levels in WT mice 48 h postreperfusion. Significantly improved hemodynamics ( +/- dP/dt, left ventricular systolic pressure, mean arterial pressure), increased rate pressure product, and reduced myocardial infarct size ( 18 +/- 2.5% vs. 31 +/- 4.6%) were found 48 h after reperfusion in eNOS(-/-) mice compared with WT mice. Myocardial infarct size was also significantly decreased in WT mice treated with the specific iNOS inhibitor 1400W ( 20.5 +/- 3.4%) compared with WT mice treated with PBS ( 33.9 +/- 5.3%). A marked reperfusion- induced hyperoxygenation state was observed by electron paramagnetic resonance oximetry in postischemic myocardium, but P-O2 values were significantly lower from 1 to 72 h in eNOS(-/-) than in WT mice. Cytochrome c- oxidase activity and NADH dehydrogenase activity were significantly decreased in postischemic myocardium in WT and eNOS(-/-) mice compared with baseline control, respectively, and NADH dehydrogenase activity was significantly higher in eNOS(-/-) than in WT mice. Thus deficiency of eNOS exerted a sustained beneficial effect on postischemic myocardium 48 h after reperfusion with preserved mitochondrial function, which appears to be due to decreased iNOS induction and decreased iNOS- derived peroxynitrite in postischemic myocardium.