Effect of meclastine, an H1-antihistamine, on plasma ACTH in adrenal insufficiency.

In order to evaluate the possible role of endogenous histamine in ACTH secretion we investigated the effect of the H1 antagonist meclastine on plasma ACTH in patients with ACTH hypersecretion. Seven patients with primary adrenal insufficiency (group 1) and 5 patients with ACTH dependent Cushing's syndrome (group 2) were given an iv infusion of meclastine (4.8 mg/90 min). In patients of group 2 plasma ACTH was unaffected by meclastine infusion. However, in patients of group 1 with intact steroid feedback meclastine was followed by a significant drop in plasma ACTH as compared with ACTH levels after saline infusion (46.0 +/- 4.6% vs 85.0 +/- 7.0%, P less than 0.01). These results suggest that histamine is involved in the control of ACTH secretion, possibly by stimulation of CRF release.