Effect of L-canavanine, an Inhibitor of inducible nitric oxide synthase, on myocardial dysfunction during septic shock.

Overproduction of nitric oxide (NO) by inducible NO synthase (iNOS) plays a role in the pathophysiology of septic shock. The depression of cardiac contractility in such situations is mediated by proinflammatory cytokines, including interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha). The effects of two NOS inhibitors with different isoform selectivity were compared in isolated working rat hearts. The depression of contractility by IL-1beta and TNF-alpha was prevented by administration of a nonselective nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) or an inhibitor of inducible nitric oxide synthase, L-canavanine. In contrast, when L-NAME was administered in the absence of IL-1beta and TNF-alpha, it depressed contractility over the 2h perfusion period by significantly reducing coronary flow. These results support current thinking that the depression of myocardial function by IL-1beta and TNF-alpha is mediated, at least in part, by an intracardiac increase in inducible nitric oxide synthase, and that in contrast to L-NAME, the decline in coronary conductance seen in cytokine-treated is not prevented by L-canavanine hearts. L-canavanine shows selective inhibition of inducible nitric oxide synthase unlike the vasopressor action of L-NAME in cytokine-treated hearts.