AND BRAUNWALD, E.: Studies on digitalis XIV: Influence of cardiac norepinephrine stores on the response of isolated heart muscle to digitalis. Circ Res 19

On the basis of studies on cardiac tissue removed from animals treated with antiadrenergic drugs, a number of investigators have suggested that the posi-tive inotropic response to digitalis requires norepinephrine in the cardiac mus-cle. In the present study the action of strophanthidin was studied in isolated papillary muscles obtained from normal cat hearts, from chronic, totally car-diac-denervated, norepinephrine-depleted hearts, and from reserpine-treated, norepinephrine-depleted cats. Complete force-velocity and length-tension curves were recorded. Following the addition of strophanthidin (1.0/xg/ml) to the bath, maximum isometric tension rose by averages of 2.17 ±0.32 g/mm2 in the normal muscles and 2.65 ±0.50 g/mm2 in the muscles from the de-nervated cats, but increased significantly less (P<0.05) in the muscles from the reserpine-treated animals (1.09 ±0.36 g/mm2). In addition to these changes in isometric tension, strophanthidin increased the maximum velocity of contraction (VmBI) to a comparable extent in normal and denervated mus