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Published on: April 25, 2016
ACTH precursors characterize the ectopic ACTH syndrome
P M Stewart1, S Gibson, S R Crosby
1Department of Medicine, University of Birmingham, UK.
Clinical Endocrinology
|February 1, 1994
Summary
Ectopic ACTH syndrome is characterized by elevated ACTH precursors, not mature ACTH. These precursors, rather than ACTH, correlate with cortisol levels and dominate circulation.
Area of Science:
- Endocrinology
- Oncology
Background:
- Adrenocorticotropic hormone (ACTH) is secreted by the pituitary after processing of precursors like proopiomelanocortin (POMC).
- Ectopic ACTH syndrome involves ACTH secretion by non-pituitary tumors, but the primary circulating peptide form is often unclear.
Purpose of the Study:
- To investigate the predominant circulating form of ACTH and its precursors in ectopic ACTH syndrome.
- To compare peptide profiles in ectopic ACTH syndrome with pituitary-dependent Cushing's syndrome and controls.
Main Methods:
- Compared plasma ACTH and precursor levels in 15 ectopic ACTH syndrome patients, 20 Cushing's disease patients, 22 small cell lung carcinoma patients, and 25 controls.
- Utilized specific monoclonal-based immunoradiometric assays for peptide measurement.
- Performed serial measurements and chromatographic analysis in select cases.
Main Results:
- ACTH precursors were significantly elevated in ectopic ACTH syndrome compared to all other groups (P < 0.001).
- ACTH levels were elevated but less so than precursors; secretion was non-pulsatile in ectopic cases, unlike Cushing's disease.
- ACTH precursors, not ACTH, correlated with plasma cortisol in ectopic ACTH syndrome; chromatographic analysis confirmed precursors as the dominant circulating form.
Conclusions:
- Ectopic ACTH secretion is marked by aberrant POMC processing, with precursors being the predominant circulating form.
- The condition should be termed 'ectopic ACTH precursor syndrome' for greater accuracy.
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