Human corticotropin (ACTH) radioimmunoassay with synthetic 1--24 ACTH.

A corticotropin antiserum was obtained from rabbits immunized with synthetic 1--24 corticotropin conjugated with bovine serum albumin. The antiserum did not cross react with synthetic alpha-melanotropin or with synthetic beta-endorphin and had a cross reactivity of 0.23% with human beta-lipotropin. We developed a radioimmunoassay with the antiserum obtained, in which we used polyethylene glycol in conjunction with a second precipitating antibody for fast (15-min) separation of antibody-bound and free corticotropin. The assay had a sensitivity of 16 ng/L and was validated on patients with various pituitary and adrenal diseases. From 103 normal subjects, the median value for corticotropin in specimens collected during the morning was 34 ng/L of plasma; the upper 95% confidence limit of the normal range was 98 ng/L.