Inhibition of Thyrotropin- and Dibutyryl Cyclic AMP-Induced Secretion of Thyroxine and Triiodothyronine by Catecholamines12

Abstract

Thyrotropin (TSH), 1 mU[milliunits]/ml and N6, O2''-dibutyryl 3'',5''-cyclic AMP (dbcAMP) greatly enhanced the release of thyroxine (T4) and triiodothyronine (T3) from mouse thyroids incubated in vitro. L-Epinephrine (E) and L-norepinephrine (NE) strongly inhibited the TSH and dbcAMP-stimulated release of thyroid hormones; L-isoproterenol (IPNE) exerted a relatively weak inhibition. The inhibition by catecholamines was prevented by the .alpha.-adrenergic blocker, phentolamine; L-propranolol, a .beta.-adrenergic blocker, had no effect on the inhibition. The TSH-induced release of thyroid hormones was not affected by adrenergic blockers. Epinephrine did not affect the increase in thyroidal cAMP content induced by TSH. Catecholamines act by way of an .alpha.-adrenergic receptor to suppress TSH-stimulated release of thyroid hormones at a point beyond cAMP formation.