Pharmacodynamic Effects of Beta-Adrenergic Receptor Blockade in Patients with Hyperthyroidism *

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Abstract
This study was designed to explore the part which beta-adrenergic receptor activity plays in the accelerated cardiac output and tachycardia of hyperthyroidism. Hemodynamic responses to beta-adrenergic receptor stimulation by graded doses of isoproterenol were recorded in 7 hyperthyroid patients before and after intravenous nethalide (1 mg/kg intravenously) and before and 3 to 7 days after oral nethalide (600 to 800 mg/day). Despite inhibition of the chronotropic and inotropic effects of isoproterenol, nethalide did not significantly change O2 consumption, heart rate, cardiac output, systemic mean arterial or mean right atrial pressures in these patients. Three additional hyperthyroid patients had similar measurements before and after intravenous saline solution or nethalide placebos in order to assay the effects of passage of time. Saline solution or nethalide placebo did not alter the responses to isoproterenol. These findings do not support the hypothesis that the hemodynamic changes in hyperthyroidism are mediated through adrenergic stimulation of beta-adrenergic receptors.