Time-dependent expression pattern of nitric oxide and superoxide after myocardial infarction in rats

Previous experiments by our group have demonstrated a subacute increased contribution of nitric oxide (NO) to vasoreactivity after myocardial infarction in rats. However, the activation pattern of NO may be phasic after infarction and has been described to be strongly associated with superoxide production. Therefore, the present study evaluated the morphological distribution and time-dependent induction of NO and superoxide at the protein (via immunohistochemistry, chemiluminescence and spectrophotometry) and mRNA (via real-time RT-PCR) level after experimental induction of a myocardial infarction in rats. Myocardial infarction led to a modest but lasting upregulation of endothelial NO synthase (eNOS) in blood vessels and cardiomyocytes. In contrast, inducible NOS (iNOS) showed dramatic de novo formation 1 week after infarction, predominantly in the infarcted area and cardiomyocytes. In addition, a gradually increased myocardial production of superoxide was detected during remodelling, probably related by an upregulation of NADH oxidase in the peri-infarcted and remote myocardium. Furthermore, peroxynitrite formation was increased after myocardial infarction, indicating strong interaction between NO and superoxide. In conclusion, during the early remodelling phase after myocardial infarction mRNA concentrations and protein levels of eNOS and iNOS show an augmentation in a biphasic manner. Moreover, upregulation of NADH oxidase leads to increased presence of superoxide and peroxynitrite and thereby to a reduction of the bioavailability and compensatory effects of NO, as such influencing post-infarction remodelling.