Plasma calcitonin response to a calcium clamp in endogenous Cushing's syndrome.

Basal and calcium (Ca) stimulated plasma CT concentrations have been studied in 6 premenopausal females with Cushing's disease and 3 premenopausal females with Cushing's syndrome due to an adrenocortical adenoma. Thirteen healthy premenopausal females served as a reference group. A standardized Ca-stimulus was applied to all subjects by means of the 'calcium clamp' technique. Plasma immunoreactive CT (iCT) was determined by RIA using a carboxyl terminal antiserum with 8 pg-eq/ml as detection limit. The patients with Cushing's disease had normal basal plasma iCT levels and their iCT response during the 2 h calcium clamp was within the reference range in 5 out of 6 patients, the remaining patient showed a slightly exaggerated response. The patients with adrenal adenoma had elevated plasma iCT levels in the basal state but a normal response during the calcium clamp. It is therefore less likely that the bone resorption often seen in Cushing's syndrome is due to CT deficiency.