THE ROLE OF NITRIC-OXIDE IN CARDIAC DEPRESSION INDUCED BY INTERLEUKIN-1-BETA AND TUMOR-NECROSIS-FACTOR-ALPHA

1 Myocardial dysfunction during septic shock is associated with enhanc ed production of cytokines such as interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha). These cytokines depress card iac mechanical function by a mechanism which is not well defined. 2 Ba cterial endotoxin or cytokines cause the expression of Ca2+-independen t nitric oxide (NO) synthase in cardiac myocytes, vascular endothelial cells and endocardial endothelial cells, causing enhanced production of NO. As NO has negative inotropic actions on cardiac muscle, we test ed the sum effects of IL-1 beta plus TNF-alpha in the intact heart to determine whether enhanced expression of NO synthase activity in the c ells that comprise the heart is involved in cardiac depression associa ted with cytokine stimulation. 3 Rat isolated working hearts perfused with IL-1 beta plus TNF-alpha showed a markedly greater depression in contractile function, measured as cardiac work, after 2 h of perfusion compared with time-matched control hearts. The depressant action of I L-1 beta plus TNF-alpha was first apparent after 1 h of perfusion; no early (15 min) cardiac depressant actions were seen. 4 The competitive inhibitor of Ca2+-dependent and Ca2+-independent NO synthases, N-G-ni tro-L-arginine methyl ester (L-NAME, 3 mu M) when given concurrently w ith IL-1 beta plus TNF-alpha prevented the loss in contractile functio n such that these hearts after 2 h of perfusion had similar function t o time-matched controls. L-NAME did not acutely reverse the loss of co ntractile function in hearts exposed for 2 h to IL-1 beta plus TNF-alp ha. The protective action of L-NAME in the presence of cytokines was c oncentration-dependent and was not seen at a higher concentration (10 mu M) due to the significant reduction in coronary flow observed at th is concentration. 5 In contrast, when L-NAME (3 mu M) was given in the absence of IL-1 beta plus TNF-alpha it depressed contractile function over the 2 h perfusion period by significantly reducing coronary flow . 6 Inhibition of protein synthesis with cycloheximide (Cx) abolished the loss in function that occurred over 2 h in both control and IL-1 b eta plus TNF-alpha-treated hearts. 7 Inducible, Ca2+-independent NO sy nthase activity was not observed in freshly isolated hearts but was ob served in control hearts perfused for 2 h in vitro and-was doubled in hearts perfused with IL-1 beta plus TNF-alpha Cx prevented the express ion of Ca2+-independent NO synthase in both control and cytokine-treat ed hearts. 8 In summary, these results suggest that the depression of myocardial function by IL-1 beta plus TNF-alpha is mediated, at least in part, by induction of Ca2+-independent NO synthase activity in the heart.