Catecholamine inhibition of thyrotropin-induced secretion of thyroxine: mediation by an alpha-adrenergic receptor.

Thyroxine secretion by mouse thyroid gland incubated in vitro was measured. Thyrotropin or dibutyryl cAMP increased thyroxine secretion several-fold. l-Epinephrine and l-norepinephrine strongly inhibited this stimulated release; l-isoproterenol was relatively ineffective. Phentolamine prevented the inhibition by catecholamines of thyroxine release; l-propranolol had no effect. These findings indicate that stimulation of alpha-adrenergic receptors opposes the action of thyrotropin in the regulation of thyroxine secretion.