A NEW RADIORECEPTOR ASSAY FOR MEASUREMENT OF NATURAL AND SYNTHETIC GLUCOCORTICOIDS

Abstract

Common assays for determining plasma cortisol detect natural but not synthetic glucocort icoids. We have developed a radioreceptor assay that measures the glucocorticoid activity of both natural and synthetic steroids. Ethanol extracts of 0.05 ml of plasma are tested for their ability to inhibit 3H-dexamethasone binding to glucocorticoid receptors from cultured hepatoma cells using a charcoal absorption technique. Competition relative to cortisol (100) is: dexamethasone 945, 9<-fluorocortisol 573, corticosterone 370, triamcinolone acetonide 405, prednisolone 232, 11-deoxycorticosterone 45, aldosterone 57, 11-deoxycortisol 23, progesterone 12, cortisone 2. The assay accurately measures cortisol at 0.5μg/100 ml or dexamethasone at 0.05μg/100 ml. Glucocorticoid values generally correlate with plasma cortisol levels determined by the fluorometric and transcortin binding assays. This supports the idea that cortisol is ordinarily the major source of glucocorticoid activity in man. The assay detects the expected increase in glucocorticoid activity in plasma of patients receiving synthetic steroids and has been useful in diagnosing factitious Cushing's syndrome. Thus, the radioreceptor assay is a simple test either for determination of the level of any synthetic glucocorticoid or for evaluation of adrenal function.