β-Lipotropin and cortisol responses to an intravenous infusion dexamethasone suppression test in Cushing's syndrome and obesity

An iv infusion dexamethasone (Dex) test was used to investigate the ACTH feedback response in 9 normal subjects, 12 obese patients, and 11 patients with Cushing's syndrome. Dex phosphate was infused iv for 4 h, starting at 1100 h (1 mg/h). Plasma concentrations of /3-lipotropin (βLPH) and cortisol were measured every 20 min between 0900 and 1600 h, then every 2 h until midnight and at 0900 h the next day. In normal subjects and obese patients, plasma 0LPH and cortisol concentrations fell rapidly to less than 40 ng/liter and 3 Mg/dl, respectively, at the end of Dex infusion. Subsequent values remained low through 0900 h the next day. In 7 patients with Cushing's disease, basal plasma βLPH and cortisol concentrations declined by greater than 50% during the Dex infusion. In these patients, rapid escape from suppression occurred between 1600 and 2400 h; by 0900 h the following day, βLPH and cortisol levels were higher than 100 ng/liter and 10 Mg/dl. respectively. In 3 patients with adrenal tumors, βLPH concen...