Abstract

Dogs were surgically prepared for continuous measurement of left ventricular pressure, left ventricular diameter and pulse rate. These and other derived parameters of left ventricular function were recorded during continuous intravenous infusion of epinephrine or levarterenol (l-norepinephrine) at least four days after surgery. Effects of the two drugs at three equimolar concentrations were studied in the conscious dog and again after anesthesia by sodium pentobarbital. Pulse rate was decreased by levarterenol both in the conscious and anesthetized animal. Epinephrine decreased pulse rate in the conscious state but caused tachycardia during anesthesia. Left ventricular systolic pressure was increased in proportion to concentration by both drugs in the conscious and in the anesthetized dog, but the effect of levarterenol was the more intense. Left ventricular stroke change was increased by both drugs in proportion to concentration; the most intense effect was exerted by epinephrine during anesthesia. Diastolic diameter increased in response to both drugs to about the same extent. Systolic diameter changes were more variable. Pressure-diameter loops (stroke work) were increased in area by both drugs and to a similar degree. The amount of change relative to control was greatest during anesthesia. There was no suggestion of major differences between the effects of the two drugs on ventricular contractility.