Effect of beta-blocking agents in hyperthyroidism.

Propranolol modifies peripheral thyroxine metabolism, in opposition to the beta blocking agent GYKI 41099 which has no such effect. Both beta-receptor blockers produce a significant fall in the serum cAMP level of hyperthyroid subjects. It is suggested that the beneficial effect of the beta-blocking agents in hyperthyroidism is partly due to their depressive effect on cAMP production. As far as the action of propranolol is concerned, it may well involve an additional effect on T4 metabolism.