Studies of catecholamine effect on cyclic AMP in human cultured thyroid cells: their interaction with thyrotrophin receptor

Even though adrenergic nerve terminals between and around thyroid follicles and catecholamine stimulation of thyroid adenylate cyclase have been reported, there is no uniform concept on catecholamine interaction with thyrotrophin (TSH) receptors. Therefore, the effect of catecholamines on TSH-stimulated cyclic AMP (cAMP) accumulation in human follicular thyroid cells has been investigated, to thus eliminating the extrathyroidal actions of catecholamines. Epinephrine, norepinephrine and isoproterenol appeared to be rapid and potent stimulators of intracellular cAMP accumulation, the half maximum increase doses being 4 × 10−7m, 1 × 10−5m and 5 × 10−7m, respectively. While propranolol (1 × 10−5m) prevented the stimulatory effect of catecholamines and failed to inhibit the effect of bovine TSH, phentolamine (1 × 10−5m) enhanced the potency of norepinephrine and bovine TSH, leaving that of epinephrine unchanged. The effects of epinephrine (2 × 10−8m) and isoproterenol (2 × 10−8m) were additive to that of bovine TSH (0.5 mU/ml), but the effect of simultaneous stimulation with norepinephrine (5 × 10−7m) and bovine TSH (0.5 mU/ml) was lower than expected. Prenalterol, a selective β1-agonist, did not stimulate cAMP accumulation, while terbutaline, a selective β2-agonist, exerted a potent stimulation. Metoprolol, a selective β1-adrenergic blocker, did not affect the response of thyroid follicular cells to isoproterenol. These results demonstrate the existence of β-adrenergic receptors in human thyroid follicular cells, mainly of the type β2, apparently not correlated with TSH receptor. The existence of α-adrenergic receptors which counter-regulate TSH functional responses in human thyroid follicular cells is suggested.