Different effects of propranolol, alprenolol, sotalol, atenolol and metoprolol on serum T3 and serum rT3 in hyperthyroidism.

Serum T4, T3, rT3 and T3 resin uptake (T3 RU) were measured before and after 7 days of treatment with either propranolol, alprenolol, sotalol, atenolol or metoprolol in hyperthyroid patients. We found a significant decrease in serum T3 after propranolol, alprenolol, atenolol and metoprolol but no change in the sotalol treated group. A significant increase in rT3 was found in the propranolol and alprenolol treated groups whereas a significant fall in rT3 was found in the atenolol and metoprolol treated groups. No change was found in the sotalol treated group. The changes observed in serum T3 and in rT3 could be explained by an inhibition of the 5'deiodinase enzyme by propranolol and alprenolol and an inhibition of both the 5'deiodinase and 5 deiodinase enzymes caused by atenolol and metoprolol.