Failure of propranolol to alter thyroid iodine release, thyroxine turnover, or the TSH and PRL responses to thyrotropin-releasing hormone in patients with thyrotoxicosis.

A dual isotope method allowing simultaneous analysis of both endogenous thyroidal release and peripheral thyroxine disposal was employed in four patients with thyrotoxicosis before and during propranolol therapy (160 mg/day) to determine whether beta adrenergic blockade with this agent affected the secretion or metabolism of thyroid hormone. Since catecholamines may be involved in the regulation of both thyrotropin (TSH) and prolactin (PRL) release from the pituitary, the effect of propranolol on the TSH and PRL responses to thyrotropin-releasing hormone (TRH) was also examined. In the dosage employed in these patients, propranolol had no demonstrable effect on either thyroid hormone secretion, the peripheral disposal of T4, or the TSH and prl responses to TRH.