The NADH oxidases are regulated by a variety of pathophysiological stimuli, including ANGII, hemodynamic forces, and inflammatory cytokines. TNF is involved in myocardial release of free radicals via a self-amplifying process, as production of free radicals has been shown to further increase TNF. Further, TNF interactions with ANGII seem to be mediated by an overproduction of ROS through modulation of vascular NADH oxidase activity and expression. Here, we report that AT-1R activation plays an important role in peroxynitrite production, and that AT-1R blockade reduces peroxynitrite production. Although LOS produces its beneficial effects via inhibition of AT-1R, the exact molecular mechanism contributing to these effects is still unclear. We have shown that TNF markedly decreased both endothelial nitric oxide synthase expression and mitochondrial biogenesis in TNF-treated rats. Thus, our findings are in agreement with those of earlier publications demonstrating that ANGII regulates NOS expression, modulates nitric oxide levels, and activates eNOS through AT-1R. Consistent with previous studies, TNF increased AT-1R gene expression in rats given TNF, which led to upregulation of the NADH oxidase subunit gp91phox. This, in turn, stimulated ROS formation. These effects were attenuated by AT-1R blockers. Our results demonstrate that TNF interacts with ANGII via an increased functional AT-1R level in the LV, suggesting that, in addition to its direct cellular effects, ANGII might also enhance responsiveness to TNF and thus alter cardiac function. TNF administration also upregulated the expression of inducible NOS. This is probably because the iNOS gene is regulated by the transcription factor, NF-kB, which is known to respond to as well as induce, TNF production. Upon activation by TNF and/or ANGII, NF-kB translocate from the cytosolic compartment to the nucleus, where it binds to the iNOS gene promoter and ultimately triggers iNOS gene transcription. This process is mediated by kinase-mediated protein phosphorylation and requires disassociation between NF-kB and its native inhibitor IkB. It is already known that induction of iNOS decreases NO bioavailability and increases Doxorubicin 25316-40-9 superoxide and peroxynitrite/nitrotyrosine formation in the heart, which partially explains NO dysregulation in rats given TNF. Here, we report that TNF and ANGII interact to cause oxidative stress and result in the increased production of superoxide, which reacts with nitric oxide to produce peroxynitrite. This peroxynitrite can, in turn, cause mitochondrial damage by several mechanisms that include superoxide- and hydrogen peroxide-induced damage to respiratory complexes and depletion of ATP synthesis. Increased iNOS expression and peroxynitrite production formation have been observed in rats after TNF treatment. Higher NO production via iNOS has been shown to be associated with the pathogenesis of cardiac dysfunction and heart failure. We did detect an increase in iNOS mRNA and peroxynitrite formation in the hearts of rats treated with TNF, and these increases in iNOS expression, ROS production, superoxide generation, and peroxynitrite formation were accompanied by a marked loss of mitochondrial genes, whereas these changes were attenuated in TNF +losartan treatment with preservation of cardiac function. In the present study, we have also shown that TNF- a markedly decreased both eNOS expression and mitochondrial biogenesis in LV of TNF treated rats.