Role of nitric oxide in the myocardial injury of myocarditis and myocardial ischemia

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This study was designed to investigate the role of nitric oxide (NO) in the pathogenesis of myocardial injury in myocarditis and myocardial ischemia by the methods of histopathology, immunohistochemistry, histochemistry and molecular biology. The amount of NO was distinctively increased in the serum and the heart tissue as well as that of TNFa and IL-1b in association with the severe histopathologic findings of the myocardium in rat myocarditis. Inducible NO synthase (iNOS) protein and mRNA were strongly expressed in the macrophage, endotheium and myocardial cells in the inflammatory lesion. Superoxide was massively detected in the heart by the methods of chemiluminescence and histochemistry. Immunohistochemical examination revealed positive reactivity for nitrotyrosine in the inflammatory lesion of the myocardium, suggesting that peroxynitrite contributes to the tissue damage. The extension of myocardial injury was significantly inhibited in the myocarditis rat administered with aminoguanidine, an inhibitor of iNOS.The myocardium with acute infarction from rat with coronary artery ligation showed positive reactivity for iNOS by the method of immunohistochemistry. Nitrotyrosine was also positive in the affected area of the myocardium. These results suggest that excess amount of NO plays an important role in the progression of myocardial injury in myocarditis and myocardial ischemia.