The short metyrapone test: comparison of the plasma ACTH response to metyrapone with the cortisol response to insulin-induced hypoglycaemia in patients with pituitary disease.

After a single dose of 2 g metyrapone given with a snack at 2300 h, blood was taken for estimation of plasma adrenocorticotrophin hormone (ACTH) concentrations at 0800 h the next morning from normal individuals and from patients with pituitary disease. Plasma ACTH concentrations following metyrapone were significantly lower in patients with pituitary disease with no evidence of anterior pituitary hormone deficiency (mean 90.0 +/- SD 63.9 ng/l) when compared with normal individuals (mean 182.5 +/- SD 14.1 ng/l, P leads than 0.01) but significantly greater than in patients with pituitary disease in whom a deficiency of one or more anterior pituitary hormones was demonstrated (mean 50.8 +/- SD 14.1 ng/l, P less than 0.01). It is concluded that the short metyrapone test is a sensitive method of detecting minor degrees of impairment of the negative feedback control of aCTH secretion that would be unrecognized by conventional assessment by insulin-induced hypoglycaemia. The clinical relevance of impaired ACTH release in response to a single dose of metyrapone in patients with pituitary tumours, in whom pituitary function is otherwise shown to be adequate, needs to be determined.