RADIOIMMUNOASSAY FOR STEROID HORMONES Ⅱ. RADIOIMMUNOASSAY FOR PLASMA CORTICOSTERONE
A radioimmunoassay for human plasma corticosterone has been developed. Antiserum against corticosterone was raised in rabbits immunized with corticosterone-21-hemisuccinate conjugated to bovine serum albumin. 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 0.1 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 subjccts. Plasma corticosterone increased 5.2 times as much as basal values after ACTH stimulation, whereas in radioimmunoassay cortisol increased as much as 2.4 times. On the other hand, plasma corticosterone decreased to 22.6 % of basal values at four hours after the administration of 1 mg dexamethasone, whereas by the radioimmunoassay cortisol decreased to 12.3 % of basal values.