Temperature-dependent inotropic effects of lignocaine and ethanol on rat heart papillary muscles

1. The main objective of the present study was to investigate the temperature dependence of the cardiac inotropic effects of lignocaine and ethanol (EtOH). 2. We studied the in vitro inotropic actions and interactions of EtOH (2.4 g/L) and lignocaine (25 mg/L) on rat papillary muscles superfused with Tyrode's solution and stimulated at 1 Hz at either 37 or 30 degrees C. Peak tension developed (PTD), maximum velocity of development of tension (VmaxT) and time to peak tension (TPT) were measured. 3. At 37 degrees C, EtOH depressed PTD, while VmaxT and TPT remained unchanged. At 37 degrees C, lignocaine alone or in combination with EtOH depressed all three parameters. 4. At 30 degrees C, EtOH did not modify PTD or VmaxT, whereas TPT decreased. At 30 degrees C, lignocaine decreased TPT, but VmaxT did not change and the effect of lignocaine on PTD was smaller at 30 degrees C than at 37 degrees C. Ethanol and lignocaine in combination decreased all three parameters at 30 degrees C. However, the depression of VmaxT by the combination of lignocaine and EtOH was less at 30 degrees C than at 37 degrees C. 5. Hypothermia (30 degrees C) protected the myocardium against the depressant actions of EtOH and lignocaine, alone or in combination. With EtOH alone, the protection resulted in no change in PTD. When lignocaine was involved, the protection resulted in a weaker action on PTD and VmaxT. The temperature dependence of the action of lignocaine may explain, at least in part, the development of ventricular failure in cardiac surgical patients exposed to lignocaine during hypothermia and rewarming.