Human Plasma Immunoreactive Lipotropin and Adrenocorticotropin in Normal Subjects and in Patients with Pituitary-Adrenal Disease*

Abstract

In view of current evidence indicating that ACTH and lipotropin (LPH) are synthesized in the form of a common precursor molecule, plasma ACTH and LPH concentrations were measured simultaneously to determine if such concentrations vary concomitantly. Studies were performed in normal subjects under basal conditions and those of pituitary-adrenal stimulation (insulin-induced hypoglycemia and Pitressin administration) and suppression (dexamethasone administration). Patients with pituitary-adrenal disease (Cushing''s disease, Nelson''s syndrome and Addison''s disease) were studied under basal and circadian conditions and during pituitary suppression. In normal subjects, basal plasma LPH concentrations at 0800-0900 h were 6.6 .+-. 0.5 f[femto]mol/ml; those of ACTH were 19.4 .+-. 1.7 fmol/ml. Effective hypoglycemia or Pitressin administration resulted in parallel rises in plasma ACTH and LPH concentrations. Plasma ACTH and LPH concentrations at 0900 h declined significantly after midnight dexamethasone administration. Basal levels of LPH and ACTH were markedly increased in patients with Nelson''s syndrome (LPH, 655 .+-. 34 fmol/ml; ACTH, 1028 .+-. 240 fmol/ml), or Addison''s disease (LPH, 189 .+-. 16 fmol/ml; ACTH, 175 .+-. 7 fmol/ml), and were significantly increased in patients with Cushing''s disease (LPH, 20.3 .+-. 7.5 fmol/ml; ACTH, 38 .+-. 17 fmol/ml). There was concomitant episodic ACTH and LPH secretion in patients with Nelson''s syndrome. Elevated levels of LPH and ACTH in a patient with Addison''s disease declined in parallel after hydrocortisone administration. A significant correlation (4 [correlation coefficient] = 0.9638; P < 0.001) was present between plasma ACTH and LPH concentrations in normal subjects and patients. Both hormones seem to be simultaneously secreted.