Influence of the sympathetic nervous system on the response of the normal heart to digitalis

In experiments designed to clarify the effects of glycoside on the normal heart, acetyl strophanthidin was found to increase myocardial contractility, as reflected by the relation of stroke work to left ventricular end-diastolic pressure in dogs deprived of autonomie control of cardiac performance by ganglionic blockade and chronic cardiac denervation. Reflexly intact animals showed no consistent change in left ventricular end-diastolic pressure at constant arterial pressure, cardiac output and heart rate. All animals receiving the glycoside demonstrated a significant increase in maximal rate of rise of left ventricular pressure. Peripheral vascular resistance following the glycoside increased only in animals whose peripheral autonomie reflexes were abolished by ganglionic blockade. These data indicate that the direct inotropic effect of the glycoside on the normal heart may be obscured in the intact animal by a reflex withdrawal of cardiac sympathetic tone. The data support the position that there is no fundamental difference in glycoside action on the normal versus the failing heart.