A Radioimmunoassay for Human Plasma Corticosterone

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Abstract
A radioimmunoassay for human plasma corticosterone was 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 [deoxycorticosteroid] and dehydrocorticosterone more than 20%. After 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 0.05-0.1 ml of plasma after microcolumn chromatography. The mean plasma corticosterone concentration at 9 a.m. was 7.1 .+-. 3.2 ng/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. Plasma corticosterone decreased to 22.6% of basal values at 4 h after 1 mg dexamethasone, whereas radioimmunoassayed cortisol decreased to 12.3% of basal values.