The value of beta-lipotrophin measurement during the short metyrapone test in patients with pituitary diseases and in Cushing's syndrome.

Abstract

Serum 11-deoxycortisol (S) determination has been used to evaluate the pituitary adrenal response to the short metyrapone (MTP) test. The validity of this indirect evaluation of corticotrophin ACTH reserve has been questioned since the MTP-induced S elevation may reflect a passive accumulation rather than an ACTH activated adrenal response. The purpose of this study was to evaluate the usefulness of serum beta-lipotrophin (beta-LPH) measurement during the short midnight MTP test (30 mg/kg body weight) in patients with pituitary diseases (n = 36) and in patients with Cushing's syndrome (n = 8). In 28/36 patients with pituitary diseases both S and beta-LPH concentrations were increased normally by MTP. In 8/36 patients the beta-LPH response was lacking, while their serum S concentrations increased significantly. The absence of beta-LPH response to MTP in these 8 patients was in good agreement with the diagnosis of ACTH insufficiency because in 7 of them the cortisol response to insulin induced hypoglycaemia was also insufficient. In the 8 patients with Cushing's syndrome serum S concentration increased following MTP administration in all the cases. In 2 with adrenal adenoma the increase of S level was an ACTH-independent phenomenon, since beta-LPH level was undetectable both before and after MTP administration. In 2 patients with ectopic ACTH secretion, the basal beta-LPH concentrations were high and remained unmodified by MTP administration. In the 4 patients with Cushing's disease, MTP administration resulted in a dramatic increase of beta-LPH concentration. We conclude that beta-LPH measurement improves the utility of the short MTP test for investigation of pituitary adrenal function.