Development of myocardial dysfunction in endotoxin shock.

Isolated heart muscle preparations were used to investigate the onset and development of myocardial inotropic dysfunction during endotoxin shock in guinea pigs. Left atrial muscles were removed from separate groups of animals at increasing time intervals after administration of either 4 mg/kg purified Escherichia coli endotoxin (shock groups) or an equivalent volume of isotonic saline (control groups). Peak developed contractile tension (CT) and maximal rate of tension development (+dT/dtmax) were significantly depressed in shock tissues as early as 2 h postendotoxin (P less than 0.01), with the magnitude of the contractile deficit progressively increasing during 4, 6, and 12 h postendotoxin. Contractility remained significantly depressed (P less than 0.001) at 16 and 24 h postendotoxin but progressively recovered toward control levels during 16, 24, 48, and 72 h postendotoxin. Shock-induced myocardial dysfunction was characterized by altered contractile responsiveness to low-Ca2+ medium (0.5 mM), gentamicin (4 mM), and hypoxia; altered inotropic reactivity to these interventions followed similar temporal development as the postendotoxin changes in basal contractile parameters. Left ventricular papillary muscles obtained at 16 h postendotoxin corroborated the shock-induced contractile depression observed in atria. These studies provide evidence for early and progressive intrinsic myocardial dysfunction in endotoxin shock and demonstrate that this dysfunction can be unmasked through the study of in vitro atrial and ventricular heart muscle preparations isolated from in vivo shocked animals.