Changes in plasma adrenocorticotropic hormone and cortisol levels induced by intracerebroventricular injection of histamine and its related compounds in dogs.

Changes in plasma adrenocorticotropic hormone (ACTH) and cortisol levels induced by intracerebroventricular injection of histamine (H(i)) were studied in dogs. Intracerebroventricular administration of Hi at doses of 5 and 10 micrograms/kg caused a significant increase in plasma ACTH, while more rapid and more marked increase in plasma cortisol was noticed after Hi injection at doses of 2-10 micrograms/kg. Similar results were obtained when 2-methylhistamine was injected; remarkable increases in both plasma ACTH and cortisol levels were observed at doses of 25 and 50 micrograms/kg. However, no such effect was elicited by 4-methylhistamine even at a dose of 50 micrograms/kg. The rate of plasma cortisol increase induced by either Hi or 2-methylhistamine was significantly faster than that of plasma ACTH. Simultaneous application of pyrilamine (intracerebroventricularly) with H(i) resulted in the significant inhibition of H(i)-induced hormone secretions, but in similar administration neither ACTH nor cortisol were affected by cimetidine. In hypophysectomized dogs, a significant increase in plasma cortisol level was also observed after H(i) injection at a dose of 5 micrograms/kg. Intravenous infusion of hexamethonium continued before and after H(i) injection failed to inhibit the increase in plasma ACTH and cortisol levels induced by H(i). From these findings, it can be concluded that intracerebroventricular injection of H(i) caused an increase in plasma ACTH and cortisol levels via H1-receptor, and it is suggested that to some extent, the cortisol release elicited by H(i) is certainly produced without participation of ACTH.