PLASMA THYROXINE, 3,3′,5-TRIIODOTHYRONINE AND 3,3′,5′-TRIIODOTHYRONINE DURING 3-ADRENERGIC BLOCKADE IN. HYPERTHYROIDISM

Abstract

Plasma thyroxine (T4), 3,3′,5-triiodothyronine (T3) and 3,3′,5′-triiodothyronlne (rT3) were measured in 16 patients with Graves′ disease. Patients were studied under the following conditions: first without any treatment, then, during β-adrenergIc blockade with propranolol, and finally after euthyroldism had been attained by carbimazole. During propranolol T3–T4 ratio decreased, whereas T4 remained unchanged. After carbimazole T3–T4 ratio returned to its pretreatment value. rT3–T4 ratio showed opposite changes. These results suggest that peripheral conversion of T4 Into T3 and rT3 in hyperthyroidlsm is, at least partly, dependent on the functional status of the β-adrenergic system. Suppressed peripheral conversion of T4 into T3 during β-adrenergic blocking agents may contribute to the beneficial effects of these drugs In thyrotoxicosls.