Development of a radioreceptor assay to measure glucocorticoids

We have developed a radioreceptor assay to measure glucocorticoids. The assay employs the partially purified 95-kDa receptor isolated from human liver and purified by size fractionation on high-performance liquid chromatography (HPLC). In the assay [3H]prednisolone competes with steroids (endogenous and exogenous) for binding to the receptor. Bound and free are separated by treatment with charcoal. The between-day precision [% coefficient of variation (CV)] at concentrations of 9.4, 18.7, and 69.9 micrograms/L prednisolone is 16.6, 9.3 and 4.5%, respectively. Specificity studies revealed that hydrocortisone, deoxycorticosterone, 4-pregnene-17 alpha,21-diol-3,20-dione, 17 alpha-hydroxyprogesterone, corticosterone and beta-hydroxyprogesterone all compete with [3H]prednisolone for binding to the receptor. Prednisone and 6 alpha-methyl prednisolone displace [3H]prednisolone to only a minor degree. The assay has been used to assess "glucocorticoid activity" in children with rheumatic diseases treated with prednisolone.