Acute endotoxemia increases left ventricular contractility and diastolic stiffness in calves

We investigated the acute effects of endotoxemia on left ventricular (LV) c ontractility, relaxation, diastolic properties, and mechanical energetics i n closed-chest calves. Twelve male calves (4 to 10 days old) were anestheti zed with oc-chloralose and instrumented to measure the LV pressure-volume r elationship. Calves (n = 6) in the control group remained hemodynamically s table for 4 h, Calves (n = 6) administered endotoxin (0.1 mu g/kg, O55:B5, i.v., over 0.5 h) had increased heart rate, mean pulmonary artery pressure, LV contractility (end-systolic elastance), chamber stiffness, and mechanic al efficiency, no change in LV relaxation, and decreased mean systemic arte rial pressure, cardiac output, and LV stroke work and pressure-volume area. Endotoxin-induced changes were maximal at t= 0.5 h, after which time all h emodynamic variables gradually returned towards baseline values. Intravenou s administration of isoproterenol (0.02 mu g . kg(-1) min(-1)) alone or com bined with phenylephrine (5 mu g . kg(-1) min(-1)) at t= 4 h produced simil ar increases in heart rate, end-systolic elastance, and cardiac output in c ontrol and endotoxin-treated groups. Our findings indicate that circulatory dysfunction, rather than LV dysfunction, predominates during acute endotox emia (4 h) in chloralose-anesthetized, closed-chest neonatal calves.