Effects of histamine H1- and H2-receptor antagonists on thyrotrophin secretion in the rat

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Abstract
The effects of histamine H1- and H2-receptor antagonists on the pituitary-thyroid axis were studied in normal and thyroxine (T4)-treated rats. Acute administration (120 min before the test) of the H2 antagonist cimetidine induced a significant (P1-receptor blocker diphenhydramine (120 min before the test) was without effect. Treatment with cimetidine or ranitidine (another H2-receptor antagonist) for 5 days induced a marked decrease in basal plasma TSH concentrations (PPP4-induced suppression of plasma TSH. Administration of cimetidine or ranitidine for 5 days was followed by a reduced concentration of plasma T4 and tri-iodothyronine (T3) (PP2-receptor blockers, and may indicate that histamine can physiologically regulate TSH and prolactin secretion through H2 receptors in the anterior pituitary. The results, however, do not disprove a central action of histamine, since the decreased plasma TSH concentrations in the presence of low plasma T4 and T3 concentrations, and also the decrease in plasma prolactin concentrations induced by cimetidine, suggest reduced hypothalamic stimulation. J. Endocr. (1986) 111, 175–180