Gel chromatographic characterization of immunoreactive adrenocorticotropin in patients with ACTH hypersecretion

We investigated the molecular size of circulating immunoreactive ACTH by gel chromatography in patients with ACTH hypersecretion due to various disorders of the hypothalamic-pituitary-adrenal axis. 4 patients with Addison's disease, 2 with Nelson's syndrome, 4 with Cushing's disease, 6 with the ectopic ACTH syndrome (2 bronchial carcinoma, 1 medullary carcinoma, 1 metastatic islett cell carcinoma, 1 benign bronchial carcinoid and 1 patient with occult ectopic Cushing's syndrome) and 1 patient with hypersecretion of ACTH from a clinically nonfunctioning pituitary adenoma were studied. Analysis of the molecular size of immunoreactive ACTH was performed by gel chromatography on a Sephadex G-75 column (superfine, 100 x 1.5 cm) equilibrated with 1% formic acid. 2 ml fractions were collected and evaporated to dryness. The ACTH content of the recovered samples was determined by RIA. In Addison's disease, Nelson's syndrome and Cushing's disease the plasma showed a single peak of ACTH immunoreactivity at the expected position of 1-39 ACTH. In the ectopic ACTH syndrome the plasma of 4 patients revealed at chromatography at least one other peak eluting between the void volume and 1-39 ACTH suggestive of a high molecular weight form of ACTH whereas plasma of 2 patients showed only a single ACTH peak at the position of labeled 1-39 ACTH. The patient with a clinically non-functioning pituitary adenoma revealed a gel filtration pattern similar to the patients with ectopic ACTH syndrome and secretion of high molecular weight ACTH. We conclude that secretion of high molecular weight forms of ACTH is not a unique feature of the ectopic ACTH syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)