Evidence for the existence of a histamine H2-receptor in the mouse thyroid.

The existence of a histamine H2-receptor in the thyroid was investigated. Histamine in vitro stimulated the formation of cyclic AMP and colloid droplet formation in mouse thyroid lobes. Stimulation by histamine of cyclic AMP formation in mouse thyroid lobes was significantly inhibited by metiamide, a histamine H2-receptor antagonist. 4-Methylhistamine, a histamine H2-receptor agonist, markedly stimulated cyclic AMP formation, whereas 2-methylhistamine, a histamine H1-receptor agonist, was ineffective. The stimulation by 4-methylhistamine of cyclic AMP formation was markedly inhibited by metiamide, but not by chlorpheniramine, a histamine H1-receptor antagonist. In contrast, metiamide did not affect cyclic AMP formation induced either by TSH or by the long-acting thyroid stimulator. Therefore, it is suggested that there exists a histamine H2-receptor in the membranes of the thyroid follicular cells which facilitate thyroid hormone secretion via the adenylate cyclase-cyclic AMP system.