Role of nitric oxide and platelet-activating factor in cardiac alterationsinduced by tumor necrosis factor-alpha in the guinea-pig papillary muscle

Objective: Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytok ine with negative inotropic properties, is implicated in several pathophysi ological events. To clarify the mechanism of action of TNF-alpha on myocard ium, we investigated the possible role of platelet-activating factor (PAF) and nitric oxide (NO) as secondary mediators of the depressant effect of th is cytokine. Methods: Isometric twitches and intracellular action potential s were recorded from guinea pig papillary muscles. The effects of TNF-alpha (1-10 ng/ml) were studied in controlled conditions and after treatment wit h 0.5% Triton X-100, to destroy the endocardial endothelium. N-G-nitro-L-ar ginine methyl ester (L-NAME), D-NAME (1 mM) and the two different PAF-recep tor antagonists WEB 2170 (3 mu M) and CV 3988 (5 ELM) were used to study th e role of NO and PAF in cardiac depression induced by TNF-alpha. To study t he role of NO in cardiac alterations induced by PAF, papillary muscles were pretreated with L-NAME or D-NAME and then challenged with PAF (0.1-1 mu M) . Nitrite production by papillary muscles challenged with TNF-alpha alone, TNF-alpha in the presence of WEB 2170 or CV 3988, or PAF was studied with t he Greiss reagent method. PAF production by papillary muscles stimulated by TNF-alpha was studied by a bioassay method. Results: TNF-alpha induced an initial, transient positive inotropic effect, then reduced the contractilit y and the action potential duration in a concentration-dependent manner. Tr eatment of papillary muscle with Triton X-100 did not modify the response t o TNF-alpha, suggesting that the effect of TNF-alpha is not mediated by end ocardial endothelial cells. Pretreatment with indomethacin reduced the nega tive effect of TNF-alpha, while propranolol abolished the initial increase of contractility. The role of PAF and NO as mediators of TNF-alpha was sugg ested by: (1) the protective effect of L-NAME, but not of D-NAME, on electr ical and mechanical alterations; (2) the stimulatory effect of TNF-alpha on nitrite production; (3) the inhibitory effect of WEB 2170 and CV 3988, on both the electromechanical alterations and the nitrite production; (4) the synthesis of PAF induced by TNF-alpha. L-NAME blocked the negative effect o f PAF and PAF enhanced nitrite production by papillary muscle. Conclusions: The present results suggest that in cardiac muscle: (1) the release of PAF triggered by TNF-alpha may account for the stimulation of NO production; ( 2) both PAF and NO contribute to the development of the electrical and mech anical alterations induced by TNF-alpha; (3) NO production was down-stream to the synthesis of PAF. (C) 1999 Elsevier Science BV. All rights reserved.