CONTRACTILE DYSFUNCTION OF VENTRICULAR MYOCYTES ISOLATED FROM ENDOTOXEMIC GUINEA-PIGS

Mechanisms responsible for the decline in cardiac function following sepsis or endotoxemia are unclear but may result from indirect effects of cardiodynamic readjustments to diminishing venous return or to direct effects of endogenous factors on myocardial function. We examined contractile properties of ventricular myocytes isolated from endotoxemic guinea pig hearts to 1) verify and characterize inotropic dysfunction in the absence of immediate influences from extrinsic neurohumoral agents, and 2) assess the ability of beta-adrenergic receptor activation to modulate contractility. Myocytes were isolated by enzymatic dispersion from hearts 4 h following an intraperitoneal injection of Escherichia coli endotoxin. Contractility was assessed using a computer-driven image analysis system. Inotropic responsiveness of endotoxemic myocytes to changes in frequency of stimulation (.2-2.0 Hz) or increases in extracellular calcium ([Ca2+](o), 1.8-8.0 mM) was significantly less than control myocytes, even with maximally effective frequencies or [Ca2+](o). These data demonstrate that the endotoxin-induced dysfunction is intrinsic to ex vivo cardiac myocytes and independent of immediate influence from extracardiac factors by 4 h in vivo exposure to endotoxemia. Inotropic responsiveness to beta-adrenergic receptor activation remained intact in endotoxemic myocytes; maximally effective concentrations (>10 nM) reversed the endotoxin-induced contractile dysfunction. These data confirm that E. coli endotoxemia incorporates intrinsic contractile dysfunction of myocardial cells, while sparing their ability to respond to inotropic mechanisms activated by beta-adrenoceptor agonists.