Epinephrine Inhibits Thyrotropin-Stimulated Adenosine 3′,5′-Monophosphate Accumulation in Cat Thyroid Tissue*

Abstract

The effect of epinephrine on in vitro cat thyroid tissue cAMP accumulation was examined in both the presence and absence of added TSH. Epinephrine alone had no significant effect on cat thyroid cAMP accumulation. However, in the presence of phentolamine, an a-adrenergic antagonist, epinephrine (1 × 10⁻⁵m), elicited an increase in thyroid cAMP levels which was evident within 2 min, declining to basal levels within 10 min. In contrast, in the presence of propranolol, a β-adrenergic antagonist, the addition of epinephrine elicited a prompt 30% reduction in thyroidal cAMP levels which was sustained throughout the incubation period. Preexposure of cat thyroid tissue slices to epinephrine resulted in a significant 20−60% reduction in the subsequent TSH stimulation of cAMP accumulation and a similar reduction in the activation of cAMP-dependent protein kinase activity. A similar inhibition of TSH action was observed with norepinephrine but not with adrenochrome or dopamine. The inhibitory action of the catecholamines was reversed by washing and was abolished by phentolamine and phenoxybenzamine but not by propranolol. The inhibitory action of the catecholamines was not attenuated by the presence of phosphodiesterase inhibitors (e.g. aminophylline or isobutyl-3-methylxanthine). Moreover, epinephrine rapidly lowered thyroidal cAMP levels when it was added after the onset of TSH stimulation. These findings suggest that adrenergic mechanisms may play an important role in modulating thyroid function by reducing TSH-stimulated cAMP levels. (Endocrinology106: 28, 1980)