The measurement of acth in plasma

Abstract

An ACTH radioimmunoassay is described which provides a method for measuring ACTH concentrations in plasma over the range of 5-500pg/ml (1.1-111 pmoles/1). The ability of ACTH to adsorb strongly to glass is exploited by using a solid phase similar to glass but in a finely divided form to extract ACTH from plasma. ACTH is assayed by a classical radioimmunoassay procedure. The extraction process by removing proteolytic enzymes eliminates the need for mercapto-ethanol in the incubation medium and so enables the use of a second antibody reaction to separate free from antibody bound hormone. Studies of a commercially labelled preparation of ACTH indicated quantities of damage fragments. A much cleaner product was prepared by labelling human ACTH (1-39) by chloramine-T oxidation. Gel filtration experiments indicated the need for repurification of the tracer at fortnightly intervals.