REDUCTION OF PLASMA TRIIODOTHYRONINE (T3) INDUCED BY PROPRANOLOL

Abstract
The effect of propranolol on plasma triiodothyronine (T3), thyroxine (T4) and T3 uptake by Sephadex G-25 (RT3U%) was studied in 14 thyrotoxic patients and 8 normal volunteers. Propranolol (40 mg) as a single oral dose significantly reduced total serum T3 which began 60 min after administration. No significant changes were observed in T4 and RT3U% values. Plasma T3 levels remained suppressed during a 5 days course of treatment with propranolol. Propranolol probably has a direct effect on peripheral metabolism of T3 rather than on thyroid hormone secretion.