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Glucocorticoid-binding Components in Human Thymus Hyperplasia¹

Departments of Histology [F. O. R.], Pharmacology [M. C.], Obstetrics and Gynaecology [S. I.], and Neurology [P. T.], Catholic University School of Medicine, 644 Via della Pineta Sacchetti, 00168 Rome, Italy

Preliminary experiments on thymocyte suspensions derived from human thymus hyperplasia indicated the presence of specific cytoplasmic receptors binding [³H]dexamethasone with high affinity and specificity. The receptor was rapidly transferred into the nuclei at 28° but not at 2°. With cell-free preparations and ion-exchange cellulose-impregnated paper filters, thymus cytosol bound [³H]dexamethasone with a dissociation constant of 4.3 x 10^–9 M; the concentration of receptor sites was 9.6 x 10^–14 mole/mg cytosol protein. Cytosol contained binding components that sedimented at approximately 7S and 3.6S (low ionic strength) and at 4S (high ionic strength). Competition studies showed high specificity for glucocorticoids since binding of labeled dexamethasone was inhibited in the presence of 10^–6 M ß-methasone, prednisolone acetate, dexamethasone, corticosterone, cortisol, and cortisone. 17ß-Estradiol, testosterone, and dlhydrotestosterone at 10^–6 M did not inhibit specific binding of [³H]dexamethasone. Thus, the dexamethasone-binding components of the human thymus hyperplasia had properties similar to those described for steroid hormone receptors present in target tissues.

¹ A preliminary report of this work was presented at the Eleventh World Congress of Neurology, Amsterdam, The Netherlands, September 11 to 16, 1977 (16).

² To whom requests for reprints should be addressed.

Received 7/20/77. Accepted 11/29/77.