Myocardial ischemia/reperfusion injury in NADPH oxidase-deficient mice.

Previous studies have suggested that oxygen-derived free radicals are involved in the pathophysiology of myocardial ischemia/reperfusion (MI/R) injury. Specifically, neutrophils have been shown to mediate postischemic ventricular arrhythmias and myocardial necrosis. We hypothesized that MI/R injury would be reduced in the absence (-/-) of NADPH oxidase. Heterozygous control mice (n=23) and NADPH oxidase(-/-) mice (n=24) were subjected to 30 minutes of coronary artery occlusion and 24 hours of reperfusion. Myocardial area at risk per left ventricle was similar in heterozygous control hearts (55+/-3%) and NADPH oxidase(-/-) hearts (61+/-4%). Contrary to our hypothesis, the size of infarct area at risk was similar in the heterozygous control mice (42+/-4%) and NADPH oxidase(-/-) mice (34+/-5%) (P=not significant). In addition, echocardiographic examination of both groups revealed that left ventricle fractional shortening was similar in NADPH oxidase(-/-) mice (n=8; 27+/-2.5%) and heterozygous control mice (n=10; 23.3+/-3. 3%) after MI/R. Superoxide production, as detected by cytochrome c reduction, was significantly impaired (P<0.01) in NADPH oxidase(-/-) mice (n=6) compared with heterozygous mice (n=7) (0.04+/-0.03 versus 2.2+/-0.08 nmol O(2).min(-1).10(6) cells(-1)). Intravital microscopy of the inflamed mesenteric microcirculation demonstrated that leukocyte rolling and adhesion were unaffected by the absence of NADPH oxidase. Oyster glycogen-stimulated neutrophil transmigration into the peritoneum was also similar in both the heterozygous control mice and NADPH oxidase(-/-) mice (P:=not significant). These findings suggest that NADPH oxidase does not contribute to the development of myocardial injury and dysfunction after MI/R.