A Radioimmunoassay for Human Plasma Corticosterone

Abstract

A radioimmunoassay for human plasma corticosterone has been developed. Antiserum against corticosterone was produced in rabbits immunized with corticosterone 21-hemisuccinate conjugated to bovine serum albumin. The antiserum cross-reacted with progesterone, DOC and dehydrocorticosterone more than 20%. After the extraction with ether, and the separation by Sephadex LH-20 microcolumn chromatography, recovery was 51.2±12.1% in 50 assays. The mean coefficient of variation between assays was 7.7% and within assays was 8.6%. Human plasma corticosterone is measured readily by assaying aliquots of an ether extract of 0.05 to 0.1ml of plasma after microcolumn chromatography. The mean plasma corticosterone concentration at 9a.m. was 7.1±3.2ng/ml in 45 normal subjects. Plasma corticosterone increased 5.2 times as much as basal values after ACTH injection, whereas radioimmunoassayed cortisol increased 2.4 times. On the other hand, plasma corticosterone decreased to 22.6% of basal values at four hours after 1 mg dexamethasone, whereas radioimmunoassayed cortisol decreased to 12.3% of basal values.