Propranolol and sotalol as antagonists of isoproterenol-enhanced physiologic tremor

Six normal subjects were studied after graded bolus injections of isoproterenol. Log dose-response curves for increases in both heart rate (mostly beta 1), and amplitude of physiologic tremor (beta 2) were constructed for each subject in the control state and 2 hr after 10 or 40 mg propranolol, 200 mg sotalol, or placebo. All heart rate curves were shifted to the right in an approximately parallel fashion by all active treatments (40 mg propranolol greater than 200 mg sotalol greater than 10 mg propranolol). The tremor curve was also shifted to the right by 10 mg propranolol in an approximately parallel fashion and to the same extent as the heart rate curve (both dose-ratios = 6.1), but the tremor curves after both 40 mg propranolol and 200 mg sotalol appeared to be flattened as well as shifted laterally. We conclude that whereas it may be possible that 10 mg propranolol acts as a competitive antagonist of isoproterenol at beta 2-sites in skeletal muscle, 40 mg propranolol and 200 mg sotalol must have additional actions in reducing isoproterenol tremor. The possibilities are discussed.