Rapid endotoxin-induced alterations in myocardial calcium handling - Obligatory role of cardiac TNF-alpha

Background: Bacterial endotoxin (lipopolysaccharide [LPS]) induces septic s hock and depressed myocardial contractility. The mechanism of LPS-mediated cardiac dysfunction remains controversial. We hypothesized that LPS exerts significant effects on myocardial excitation-contraction coupling by rapid stimulation of tumor necrosis factor alpha (TNF-alpha) expression in the he art. Methods: Isolated rat hearts were studied with and without recirculation of cell-free perfusate. The effects of LPS, exogenous TNF-alpha, anti-TNF-alp ha antibody, and ceramidase inhibition were examined. Measurements included myocardial uptake of LPS, left ventricular contractility, myocardial oxyge n consumption, intracellular calcium [Ca2+] cycling, and TNF-alpha concentr ations in coronary perfusate and myocardium. Results: Lipopolysaccharide was rapidly taken tip by the perfused heart. Wi th non-recirculating perfusion, LPS had no effect on contractility, oxygen consumption, coronary vascular resistance, or intracellular free calcium co ncentration ([Ca2+](i)). However, with recirculating perfusion contractilit y was significantly impaired after 30 min of LPS, associated with lower [Ca 2+](i) levels and attenuated systolic rise in [Ca2+](i). Significant amount s of TNF-alpha accumulated in recirculating perfusate and myocardial tissue from LPS-perfused hearts. Ceramidase inhibition or neutralizing anti-TNF-a lpha antibody inhibited the effects of LPS on contractility and [Ca2+](i). Recombinant rat TNF-alpha mimicked the LPS effects with faster onset. Conclusions: Lipopolysaccharide exerts rapid, negative inotropic effects on the isolated whole rat heart. The reduction in contractility is associated with depressed intracellular calcium cycling. In response to LPS, TNF-alph a is rapidly released from the heart and mediates the effects of LPS ria th e sphingomyelinase pathway. The present study for the first time directly l inks LPS-stimulated TNF-alpha production, abnormal calcium cycling, and dec reased contractility in intact hearts.