RESUMO
Pro-inflammatory cytokines have been shown to depress myocardial mechanical function by enhancing peroxynitrite generation in the heart. The contribution of NO synthesized by different NOS isoforms, as well as the contribution of superoxide to this mechanism are still not clear. Isolated working hearts of iNOS(-/-) and wildtype mice were perfused for 120 min in the presence or absence of a mixture of pro-inflammatory cytokines (IL-1beta, TNF-alpha, and IFN-gamma). iNOS mRNA was detected only in cytokine-treated wildtype hearts. In wildtype hearts, cytokine treatment significantly decreased cardiac work, calculated as cardiac output times peak systolic pressure, to 31+/-9% of original values by the end of perfusion (P <0.05). The decline of cardiac work induced by cytokine treatment was significantly reduced in iNOS(-/-) hearts (63+/-5% of original value). Only cytokine-treated wildtype hearts showed decreased aconitase activity, indicating a higher level of oxidative stress in these hearts. Cytokines increased NADPH oxidase activity in both wildtype and iNOS(-/-) hearts, whereas NADH oxidase and xanthine oxidase/xanthine dehydrogenase activities were unaffected. The SOD mimetic MnTE2PyP prevented the cytokine-induced decline of cardiac work in both wildtype and iNOS(-/-) hearts. Cardiac p38 MAPK activation was unaltered in all experimental groups. Although genetic disruption of the iNOS gene provides partial protection against cytokine-induced cardiac dysfunction, iNOS-independent mechanisms, including contribution of NO from other NOS enzymes and the generation of superoxide, are also important contributors.