β-Lipotropin and Cortisol Responses to an Intravenous Infusion Dexamethasone Suppression Test in Cushing’s Syndrome and Obesity

Abstract

An i.v. 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 beta-lipotropin (beta LPH) 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 beta LPH and cortisol concentrations fell rapidly to less than 40 ng/liter and 3 micrograms/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 beta LPH 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, beta LPH and cortisol levels were higher than 100 ng/liter and 10 micrograms/dl, respectively. In 3 patients with adrenal tumors, beta LPH concentrations were low, and cortisol concentrations did not decline during the Dex infusion. In 1 patient with ectopic ACTH secretion, beta LPH concentrations were high and were not suppressed by the Dex infusion. We conclude that the iv infusion Dex suppression test can distinguish patients with Cushing's syndrome from normal or obese subjects and can aid in the etiological diagnosis of Cushing's syndrome.

Massive Weight Loss Decreases Corticosteroid-Binding Globulin Levels and Increases Free Cortisol in Healthy Obese Patients

“…Intravenous DEX-ST was performed as previously described (25). DEX phosphate (1 mg/h) (4 mg Soldesam; Lab Italiani Farmaceutici, Milan, Italy) was infused for 4 h beginning at 11.00 A.M.…”

“…Previous studies, which have used an oral DEX-ST to indirectly test activity of the HPA axis in obesity, found no impairment of cortisol suppression (12)(13)(14). We used intravenous DEX infusion (25) to minimize the possible alteration in oral DEX absorption and/or liver metabolism since postobese women had severe lipid malabsorption. Any attempt to explain these results should take into account that in our series, data on cortisol clearance and/or distribution volume, which can affect results, are lacking.…”

“…Moreover, estimation of free cortisol by equilibrium dialysis would be more accurate than a derivative method to assess the amount of free hormone. Additionally, we used an intravenous DEX-ST (25) to minimize the possible variations in DEX absorption in postobese women who had severe lipid malabsorption.…”

Biochemical screening for subclinical cortisol-secreting adenomas amongst adrenal incidentalomas

“…4 mg DEX test (Qualimed, Levallois Perret, France) (21). Briefly, DEX was infused for 4 h, starting at 1100 h at a rate of 1 mg/h using an i.v.…”

“…The classical 138 nmol/l threshold was used in the first instance to analyse the results of the overnight 1 mg DEX suppression test (22). In accordance with the original study of Abou Samra et al (21), the response to the i.v. 4 mg DEX test was evaluated on the 0800 h serum cortisol concentration following the infusion of DEX (normal range obtained in 12 control subjects ,27±66 nmol/l).…”