Differential regulation of nitric oxide synthase isoforms in experimental acute Chagasic cardiomyopathy

We have previously demonstrated induction and high level expression of IL-1 beta, IL-6 and tumour necrosis factor-alpha in the myocardium during the a cute stage of experimental Trypanosoma cruzi infection (Chagas' disease). T he myocardial depressive effects of these cytokines are mediated in part by the induction of nitric oxide synthase (NOS), production of nitric oxide ( NO) and formation of peroxynitrite. In this study we investigated the expre ssion, activity and localization of NOS isoforms, and the levels of NO, mal ondialdehyde (a measure of oxidative stress), and peroxynitrite in rats at 1.5, 5, 10 and 15 days after infection with T. cruzi trypomastigotes. The m yocardial inflammatory infiltrate and number of amastigote nests increased over the course of infection. A significant increase in tissue nitrate + ni trite levels, NOS2 mRNA, and NOS2 enzyme activity was observed at all time points in the infected compared with uninfected animals. The enzyme activit y of constitutive NOS, tissue malondialdehyde levels, and NOS3 mRNA levels was only transiently increased after infection. The protein levels of the N OS isoforms paralleled their mRNA expression. While no positive nitrotyrosi ne immunoreactivity was detected in control myocardium, its levels increase d in infected animals over time. Thus, by 1.5 days post-infection, when no parasite or immune cell infiltration could be detected, the myocardium expr essed high levels of NOS and NO metabolites. Nevertheless, the early produc tion of NO in the myocardium was not sufficient to clear the parasites.