1. ACTH precursors characterize the ectopic ACTH syndrome.
- Author
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Stewart PM, Gibson S, Crosby SR, Penn R, Holder R, Ferry D, Thatcher N, Phillips P, London DR, and White A
- Subjects
- Adrenocorticotropic Hormone immunology, Adult, Aged, Antibodies, Monoclonal, Carcinoma, Small Cell blood, Cushing Syndrome blood, Humans, Hydrocortisone blood, Immunoradiometric Assay, Lung Neoplasms blood, Middle Aged, Pro-Opiomelanocortin blood, Pro-Opiomelanocortin immunology, Protein Precursors immunology, Secretory Rate physiology, ACTH Syndrome, Ectopic blood, Adrenocorticotropic Hormone blood, Protein Precursors blood
- Abstract
Objective: ACTH is secreted by the pituitary following processing of larger molecular weight precursors, proopiomelanocortin and pro-ACTH. Ectopic ACTH syndrome refers to the secretion of ACTH by non-pituitary tumours, but the predominant circulating form of proopiomelanocortin-related peptides remains unclear., Patients: Fifteen patients with ectopic ACTH syndrome were compared to 20 patients with pituitary-dependent Cushing's syndrome, 22 patients with small cell lung carcinoma but no evidence of Cushing's syndrome, and 25 controls., Design and Measurements: Measurement of plasma ACTH and ACTH precursors using specific monoclonal-based immunoradiometric assays at 0900 h and, in five patients with ectopic ACTH syndrome, at 15-minute intervals for 6-24 hours., Results: ACTH precursors were grossly elevated in patients with ectopic ACTH syndrome (median 2194, range 139-18000 pmol/l) compared to patients with Cushing's disease (median 33, 8-73 pmol/l, P < 0.001), patients with small cell lung carcinomas (38, 8-117 pmol/l, P < 0.001) and controls (26, 10-39 pmol/l, P < 0.001). ACTH levels were also elevated in ectopic ACTH syndrome (0900 h median 34, 11-152 pmol/l) compared to patients with Cushing's disease (0900 h median 8, 3-19 pmol/l), but not to the same degree as ACTH precursors. In contrast with Cushing's disease, ACTH was secreted in a non-pulsatile fashion. ACTH precursors but not ACTH itself correlated with plasma cortisol in patients with ectopic ACTH syndrome (r = 0.65, P < 0.05). Chromatographic analysis of plasma from a patient with ectopic ACTH syndrome confirmed ACTH precursors and not ACTH to be the predominant circulating form. With the cross-reactivity of proopiomelanocortin and pro-ACTH in the ACTH IRMA of < 1 and < 10% respectively, ACTH precursors could represent all the ACTH immunoreactivity in patients with ectopic ACTH syndrome., Conclusions: Ectopic 'ACTH' is characterized by aberrant processing of proopiomelanocortin and should be more accurately referred to as 'ectopic ACTH precursor syndrome'.
- Published
- 1994
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