Immunocytochemical localization of corticosteroid-binding globulin in rat tissues

Previous studies utilizing steroid-binding assays have suggested that corticosteroid-binding globulin (CBG)-like glucocorticoid binding sites are present in various tissues of the rat. It is not known, however, whether such binding reflects the intracellular presence of CBG derived from serum or a special class (type III) of receptors. In order to elucidate this problem, immunocytochemical localization of rat CBG was carried out using a specific antiserum prepared against rat serum CBG and the peroxidase-antiperoxidase technique. Positive staining was found in certain cells of the liver, the distal and/or convoluted tubules of the kidney, the uterus, the follicular cells of the thyroid, and some cells of the anterior pituitary. Other tissues including heart, muscle, thymus, hypothalamus, supraoptic and paraventricular nuclei, and diaphragm were negative. The presence of immunoreactive CBG in specific cells of some glucocorticoid-responsive tissues and not others raises interesting questions concerning the transport of glucocorticoids and their mechanism of action.