Contractile function of heart muscle isolated from endotoxin-shocked guinea pigs and rats

Cardiac effects of endotoxin shock were compared in left atrial preparations isolated from guinea pigs and rats injected with 4 or 8 mg/kg E coli endotoxin. Heart muscles isolated from both species during endotoxin shock exhibited significant contractile depression which could be reversed by increasing extracellular Ca++ concentrations. Force-frequency relationships were shifted downward by endotoxin shock in both species. However, significant interspecies differences were observed in inotropic responsiveness of heart muscles isolated from shocked rats and guinea pigs. Atria from shocked guinea pigs demonstrated markedly prolonged rates of recovery from the negative inotropic effects of gentamicin (4.0 mM) and a low Ca++ medium (0.5 mM). In contrast, rates of recovery from these interventions were not altered by endotoxin shock in heart muscle from rats. Furthermore, contractile recovery from 15-min hypoxia was characterized by a significant "overshoot" phenomenon in heart muscles from shocked guinea pigs but not from shocked rats. These data suggest that although endotoxin shock produces cardiac depression in both the rat and the guinea pig, contractile responses to selected inotropic interventions are different and may reflect different cellular sites or mechanisms whereby shock produces cardiac depression in these two species.