Demonstration of Glucocorticoid Receptors in the Adrenal Cortex: Evidence for a Direct Dexamethasone Suppressive Effect on the Rat Adrenal Gland*

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Abstract
The adrenal cortex was evaluated for the presence of glucocorticoid receptors and functions. Substantial binding of [3H]dexamethasone was observed in aminoglutethimidetreated, hypophysectomized, and intact rats. Further studies demonstrated binding in cultured bovine adrenocortical cells and in Y-1 cells, a cloned murine cell line of adrenal cortical origin. Scatchard analysis of specific binding data in cytosol from hypophysectomized rats revealed an apparent Kd of ∼15 nM and a receptor content (Nmax) of 123 fmol/mg cytosol protein. Analysis of Y-1 cell cytosol showed a Kd of ∼17 nM and a Nmax of 190 fmol/mg protein. The binding site in hypophysectomized rats had the following steroid specificities: high affinity for dexamethasone, corticosterone, and progesterone; moderate affinity for 11β-cortisol, and low affinity for testosterone, estradiol, pregnenolone, and 11α-cortisol. Sedimentation in sucrose density gradients revealed 8S binding peaks in cytosols prepared from intact rat adrenal glands, Y-1 cells, and cultured bovine adrenocortical cells. Time- and temperature-dependent nuclear uptake of [3H]dexamethasone in Y-1 cells was demonstrated. In vivo treatment of hypophysectomized rats with dexamethasone significantly enhanced the rate of adrenal atrophy. ACTH stimulation tests in hypophysectomized rats showed a decreased corticosterone response in dexamethasone-treated rats compared to that in control animals. However, in vitro, there was no evidence for an effect of dexamethasone on ACTH-stimulated corticosterone production. The data indicate that the adrenal cortex possesses a high affinity binding site that fulfills the criteria for a glucocorticoid receptor. Glucocorticoid administration enhances adrenal atrophy and impairs adrenal function. We speculate that this action contributes to the suppressive effect of glucocorticoids on the pituitary-adrenal axis.