Endotoxin-induced myocardial tumor necrosis factor-alpha synthesis depresses contractility of isolated rat hearts - Evidence for a role of sphingosine and cyclooxygenase-2-derived thromboxane production

Background-Although endotoxin (lipopolysaccharides, LPS) is recognized as a mediator of septic cardiodepression, its cardiac effects are still not ful ly elucidated. Methods and Results-Perfusion of isolated rat hearts with LPS for 180 minut es resulted in a decline of left ventricular contractility after 90 minutes , whereas coronary perfusion pressure remained unaffected. This cardiodepre ssion was paralleled by a release of tumor necrosis factor (TNF)-alpha into the perfusate and preceded by myocardial TNF-alpha mRNA upregulation as qu antified by real-time polymerase chain reaction. The cardiodepression was a brogated when LPS was perfused with a TNF-alpha antiserum or the ceramidase inhibitor N-oleoylethanolamine. In contrast, the cardiac release of nitric oxide (NO) was not augmented by LPS. Immunohistochemical studies of LPS-pe rfused hearts revealed a positive staining for the constitutive (NOSIII) bu t not for the inducible NO synthase (NOSII). Accordingly, NOSII mRNA levels commenced to increase only at the very end of the LPS perfusion period. Pr ogressive liberation of thromboxane(Tx) A, and prostacyclin was induced by LPS together with myocardial cyclooxygenase (Cox)-2 mRNA expression. Both n onselective inhibition of Cox by indomethacin and selective inhibition of t he inducible Cox-2 by NS-398 abolished prostanoid release. Interestingly, t he generation of TNF-alpha and the associated cardiodepression caused by LP S were reduced by indomethacin, NS-398 and the Tx-receptor antagonist daltr oban. Conclusions-LPS depresses contractility of isolated rat hearts by inducing TNF-alpha synthesis and subsequently activating the sphingomyelinase pathwa y, whereas no evidence for a role of NOSII- or NOSIII-generated NO was foun d. Moreover, Cox-2-derived TxA(2) appears to facilitate TNF-alpha synthesis in response to LPS.