The Cardiac Effects of T3 on Ca Dependent Electrical Activities During β-Adrenoceptor Stimulation and Inhibition

Hypermetabolism, increased myocardial contractility and tachycardia which are caused by hyperthyroidism resemble the effects of sympathetic hyperactivity. We have tested the acute effects of T3 and of isoproterenol on the electrophysiological properties of isolated spontaneously beating hearts. In addition, the concentrations of the s-receptor-blocking compound (—)propranolol necessary to antagonize the electrophysiological effects of isoproterenol and T3 were also evaluated and compared to the concentration of (—)propranolol which is necessary to block the effects of isoproterenol alone.