EFFECT OF ETHANOL ON FUNCTION OF THE RAT-HEART AND SKELETAL-MUSCLES

The present study was undertaken to evaluate the acute effects of etha nol on responses of the rat heart and skeletal muscles both in vivo an d in vitro. In the anesthetized rat, intravenous infusion of ethanol a t 0.1-0.5 g/kg body weight (33-167 mM) decreased the breathing rate by 8-83%, heart rate by 4-52%, and QRS amplitude by 5-27%, and increased the P-R interval by 1-49%. In the anterior tibialis muscle subjected to repetitive nerve stimulation at 100 Hz for 0.5 sec, ethanol at 0.1 g/kg increased the amplitude of the muscle action potential (AP) by 7% , whereas at 0.5 g/kg it decreased the muscle AP by 32%. The nerve-evo ked tetanic tension was reduced by 7-34% at 0.1-0.5 g/kg ethanol. In t he isolated rat heart, perfusion of ethanol at 0.1-3.0% (22-651 mM) de creased the heart rate by 8-48% and QRS amplitude by 10-39%, and incre ased the P-R interval by 5-61%. Left ventricular pressure was increase d by 10% at 0.1% ethanol, and decreased by 80% at 3.0% ethanol. In the isolated rat phrenic nerve-diaphragm muscle preparation subjected to repetitive nerve stimulation at 100 Hz for 0.5 sec, 0.1-3.0% ethanol d ecreased the amplitude of the nerve AP by 5-89%, nerve-evoked muscle A P by 2-96%, and peak tetanic tension by 1-87%. On repetitive direct mu scle stimulation at 100 Hz for 0.5 sec, 0.1-3.0% ethanol decreased the amplitude of the muscle-evoked muscle AP by 8-65%, and muscle-evoked tetanic tension by 2-65%. These studies indicate that ethanol causes s maller reduction in responses of the heart and skeletal muscles at cli nical concentrations, but marked reduction in these responses at highe r concentrations due to direct action on excitability of these tissues . At higher concentrations, ethanol causes greater reduction in excita bility of the skeletal muscle than of the heart.