No evidence of direct cardiac action of leucine-enkephalin in canine heart-lung preparation.

Intravenous administration of leucine-enkephalin (30 micrograms/kg) caused significant decreases in mean blood pressure, cardiac output, and left ventricular dP/dt in intact dogs. However, cardiovascular effects of leucine-enkephalin (30-120 micrograms/kg) did not occur in the heart-lung preparation uninfluenced by extracardiopulmonary factors. These results provide no evidence of a direct cardiac action of leucine-enkephalin.