Plasma levels of immunoreactive corticotrophin in patients with Cushing's syndrome.

Plasma levels of immunoreactive corticotrophin (A.C.T.H.) have been determined in 56 patients with Cushing's syndrome by means of a homologous radioimmunoassay. In untreated Cushing's disease (bilateral adrenal hyperplasia due to excessive A.C.T.H. secretion from the pituitary) plasma values ranged from 40 to 200 mumug./ml., between 8 and 10 a.m., compared with a range in normal subjects of 12 to 60 mumug./ml. Considerably raised levels, often above 2,000 mumug./ml., were found in patients with Cushing's disease after bilateral adrenalectomy. A.C.T.H. concentrations were usually higher in patients with bilateral adrenal hyperplasia associated with ectopic A.C.T.H. production than in patients with untreated Cushing's disease; whereas plasma A.C.T.H. was undetectable in the presence of an adrenocortical tumour. All patients with Cushing's syndrome failed to show the normal circadian rhythm of circulating A.C.T.H. levels.