α1-adrenergic regulation of thyrotropin-stimulated release of 3, 5, 3’ -triiodothyronine and thyroxine from perifused mouse thyroid

The effect of methoxamine, a specific α-adrenergic agonist, on the release of T, T and cAMP from perifused mouse thyroid was studied to clarify the role of the α-adrenergic receptor in the regulation of thyroid hormone secretion. TSH-stimulated T and T release was inhibited significantly by methoxamine. With regard to cAMP release, methoxamine inhibited TSH-stimulated cAMP release in the presence of 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone but did not inhibit TSH-stimulated cAMP release in the presence of 3-isobutyl-1-methylxanthine. Methoxamine did significantly suppress TSH-stimulated release of T and T in the presence of each phosphodiesterase inhibitor. Depletion of Ca in the perifusion buffer abolished completely the inhibitory effect of methoxamine on TSH-stimulated T and T release. The present study suggests that activation of the α-adrenergic receptor inhibits TSH-stimulated T and T secretion through a Ca — dependent mechanism in the mouse thyroid gland.