Histamine-induced ACTH secretion and inhibitory effect of antihistaminic drugs

Concentration of adrenocorticotropic hormone (ACTH) in the serum increased and reached the maximum level 10 min after the injection of histamine (dihydrochloride, 0.5 or 1 mg/100 g) i.p. into rats. The maximum concentration of ACTH in the serum was dependent on the dose of histamine. The ACTH concentration then decreased and was close to the normal level 30 to 60 min after the injection. The ACTH secretion induced by histamine (0.5 mg/100 g) was inhibited completely by the pretreatment with the antagonists of H1-receptor, diphenyhydramine (hydrochloride, 0.2--0.5 mg/100 g), promethazine (hydrochloride, 0.1--0.2 mg/100 g) and d-chlorpheniramine (maleate, 0.02--0.05 mg/100 g). The antagonist of H2-receptor, metiamide (2--4 mg/100 g) inhibited the ACTH secretion significantly but not completely. These results suggest that H1-receptor plays a major role in the histamine-induced ACTH secretion, although H2-receptor is also involved in this ACTH secretion.