Role of nitric oxide and platelet-activating factor in cardiac alterations induced by tumor necrosis factor-alpha in the guinea-pig papillary muscle.
OBJECTIVE
Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine with negative inotropic properties, is implicated in several pathophysiological events. To clarify the mechanism of action of TNF-alpha 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-alpha (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 microM) and CV 3988 (5 microM) were used to study the role of NO and PAF in cardiac depression induced by TNF-alpha. 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 microM). 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 the 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 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-alpha, suggesting that the effect of TNF-alpha is not mediated by endocardial endothelial cells. Pretreatment with indomethacin reduced the negative effect of TNF-alpha, while propranolol abolished the initial increase of contractility. The role of PAF and NO as mediators of TNF-alpha 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-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 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-alpha 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-alpha; (3) NO production was down-stream to the synthesis of PAF.
Alloatti
G
G
Dipartimento di Biologia Animale e dell'Uomo, Università degli Studi di Torino, Turin, Italy.
Penna
C
C
De Martino
A
A
Montrucchio
G
G
Camussi
G
G
D000200:Action Potentials / Q000187:drug effects; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003864:Depression, Chemical; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010742:Phospholipid Ethers / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D014230:Triazoles / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000319:Adrenergic beta-Antagonists; D001381:Azepines; D016861:Cyclooxygenase Inhibitors; D010742:Phospholipid Ethers; D010972:Platelet Activating Factor; D010975:Platelet Aggregation Inhibitors; D014230:Triazoles; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; C037913:CV 3988; D011433:Propranolol; C063964:bepafant; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin