The determination of corticosterone concentration in rat plasma by competitive protein binding analysis

Abstract

A competitive protein binding assay for the determination of corticosterone in rat plasma is described with the criteria of sensitivity, specificity, precision and accuracy evaluated in some detail. Rat plasma corticosterone binding globulin was used as the source of binding protein to assay the mass of corticosterone in ethyl acetate extracts of rat plasma. Steroids other than corticosterone which might interfere with the determination were shown either to be ineffective in displacing the radioligand or were present in such small quantities as to be insignificant in normal rats. The procedure involved the extraction of 50 μl samples of plasma, one fifth of the extract being assayed by means of a standard curve with a range of 0–6 ng. The sensitivity of the assay was 0.77 ng/50 μl (1.54μg/100 ml) and the precision over the most commonly encountered concentration range, 10.0–20.0 μg/100 ml, was ±0.81 μg/100 ml ( N = 76).