Effect of beta-adrenergic blockade on plasma dopamine-beta-hydroxylase activity and triiodothyronine in hyperthyroidism.

The effect of propranolol on plasma dopamine-beta-hydroxylase activity and triiodothyronine was investigated in twelve subjects with Graves' disease. Plasma DBH activity, serum triiodothyronine and thyroxine were determined beforehand and electrocardiograms were recorded on the same days as the blood samples were taken. Propranolol administration was associated with clinical amelioration in blood pressure and ECG. There was a positive and significant correlation between changes in DBH activity and triiodothyronine caused by propranolol. These data offer evidence that there may be an interaction between plasma DBH activity and triiodothyronine during propranolol administration in hyperthyroidism.