Measurement of circulating corticotrophin-releasing factor in man.

A radioimmunoassay was developed to measure corticotrophin-releasing factor (CRF-41) extracted from human plasma using Vycor glass. Assay sensitivity was 20 ng/l and intra- and interassay coefficients of variation were 10.2 and 11.4% respectively. The normal range of plasma CRF-41 was less than 20-110 ng/l (n = 46). Plasma concentrations of CRF-41 in patients with Cushing's disease. Nelson's syndrome and Addison's disease were within the normal range. No correlation was found between CRF-41 and ACTH in these syndromes. Two patients with the ectopic ACTH syndrome had increased plasma concentrations of CRF-41. In normal subjects no changes in plasma CRF-41 occurred after insulin-induced hypoglycaemia, treatment with dexamethasone or feeding, and changes in the concentrations of CRF-41 did not reflect circadian changes in plasma concentrations of cortisol. Concentrations of immunoreactive CRF in plasma of women in the third trimester of pregnancy were increased (550-9300 ng/l) and gel filtration chromatography showed that this comprised CRF-41 and a higher molecular weight form. Reversed-phase high-performance liquid chromatography also revealed multiple peaks of immunoreactive CRF in extracts of plasma and placenta.