Plasma cortisol profiles in Cushing's syndrome

Plasma cortisol profiles were studied by the frequent sampling method in 5 patients with Cushing's disease (CD), 7 patients with Cushing's syndrome due to adrenocortical adenoma (AA), and one patient with bronchogenic carcinoma. Plasma ACTH was measured by radioimmunoassay at 10 min intervals in 2 of the subjects. In CD, there was distinct episodic secretion of cortisol and ACTH; the coefficients of variation about the mean plasma cortisol concentration ranged from 24 to 27%; plasma ACTH ranged from zero to 455 pg/ml with a mean of 94 pg/ml. In AA, the tumour secreted cortisol at a constant rate with little fluctuation; the coefficients of variation of plasma cortisol concentration ranged from 8 to 14%; plasma concentrations of ACTH were always near zero. In the patient with bronchogenic carcinoma, the coefficient of variation of cortisol was 14%. These results were apparent even in profiles of plasma cortisol concentrations measured over only a 6 h period. It is concluded that characteristics of plasma cortisol and ACTH secretory patterns are helpful in differentiating Cushing's syndrome of differing aetiology.