Characteristics of glucocorticoid-binding sites of rat liver: different effects of adrenalectomy on the binding.

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Abstract
Hydrocortisone (HC) in rat liver cytoplasmic fraction was bound to 3 different binding sites with high, medium and low affinity. Kd were .apprx. 2.1, 22 and 208 nM; the densities of these binding sites were .apprx. 40, 50 and 10% of total number of binding sites, respectively. The binding site for dexamethasone (DM) of the cytoplasmic fraction was the medium affinity one among these 3 components. The maximum number of binding sites (Bmax) of HC and DM was significantly increased by adrenalectomy. The Bmax of HC was about twice as great as that of DM in normal and adrenalectomized rat liver. DM inhibited 3H-HC binding in a dose-dependent manner but inhibition did not exceed 50% in either normal or adrenalectomized rats. Following adrenalectomy, the Bmax of the medium affinity-site for HC was significantly increased, while the high affinity component disappeared. By adding DM to the cytoplasmic fraction of adrenalectomized rat liver in vitro and in vivo, the Bmax of the medium affinity-site was significantly decreased and a high affinity component of HC was revealed with a significant increase in the number of binding sites. The binding site for DM is one component of the HC binding site; following adrenalectomy, the number of each type of binding site for glucocorticoids increases differently from the others.
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