An exchange assay for the cytoplasmic glucocorticoid receptor in the liver of the rat.

Cytosolic receptor for glucocorticoids can exist in either the free or bound form; assays now in use measure only the free form. In order to assay the total glucocorticoid receptor content of rat liver, free plus bound, we have developed an exchange assay wherein specifically bound [3H]dexamethasone is shown to be a valid measure of receptor in the presence of high concentrations of corticosterone. The exchange between [3H]dexamethasone and corticosterone is able to proceed because, unter the conditions of the assay, corticosterone is almost completely metabolized.