Role of nitric oxide and platelet-activating factor in cardiac alterations induced by tumor necrosis factor-α in the guinea-pig papillary muscle

Objective: Tumor necrosis factor-α (TNF-α), a proinflammatory cytokine with negative inotropic properties, is implicated in several pathophysiological events. To clarify the mechanism of action of TNF-α on myocardium, we investigated the possible role of platelet-activating factor (PAF) and nitric oxide (NO) as secondary mediators of the depressant effect of this cytokine. Methods : Isometric twitches and intracellular action potentials were recorded from guinea pig papillary muscles. The effects of TNF-α (1–10 ng/ml) were studied in controlled conditions and after treatment with 0.5% Triton X-100, to destroy the endocardial endothelium. NG-nitro-l-arginine methyl ester (l-NAME), d-NAME (1 mM) and the two different PAF-receptor antagonists WEB 2170 (3 μM) and CV 3988 (5 μM) were used to study the role of NO and PAF in cardiac depression induced by TNF-α. To study the 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 μM). Nitrite production by papillary muscles challenged with TNF-α alone, TNF-α in the presence of WEB 2170 or CV 3988, or PAF was studied with the Greiss reagent method. PAF production by papillary muscles stimulated by TNF-α was studied by a bioassay method. Results : TNF-α induced an initial, transient positive inotropic effect, then reduced the contractility and the action potential duration in a concentration-dependent manner. Treatment of papillary muscle with Triton X-100 did not modify the response to TNF-α, suggesting that the effect of TNF-α is not mediated by endocardial endothelial cells. Pretreatment with indomethacin reduced the negative effect of TNF-α, while propranolol abolished the initial increase of contractility. The role of PAF and NO as mediators of TNF-α was suggested by: (1) the protective effect of l-NAME, but not of d-NAME, on electrical and mechanical alterations; (2) the stimulatory effect of TNF-α 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-α. l-NAME blocked the negative effect of 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-α may account for the stimulation of NO production; (2) both PAF and NO contribute to the development of the electrical and mechanical alterations induced by TNF-α; (3) NO production was down-stream to the synthesis of PAF.