Effect of propranolol on thyroid homeostasis of healthy volunteers

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Abstract
Summary: The effect of propranolol on thyroid status was investigated by administering the drug in 2 therapeutic doses (80 mg b.d. and 120 mg b.d.) to 8 healthy volunteers and serially measuring total and free thyroid hormones and their major binding protein. Mean free T3 fell by 1.2 pmol/l (P < 0.05) whilst mean free T4 and mean rT3 rose by 3.3 pmol/l (P < 0.01) and 0.16 nmol/l (P < 0.01) respectively. Mean thyroxine binding globulin (TBG) fell by 1.2 mg/l (P < 0.001). Despite the change in free hormone levels there was no significant change in TSH. For the first time the effect of propranolol on circulating thyroid hormones and binding proteins in healthy subjects is apparent within one study. The biological significance of the change in free hormone levels is discussed.