H. Fujii-Hanamoto, K. Seiki, K. Sakabe
Nov 1, 1985
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Journal
The Journal of endocrinology
Abstract
By using the synthetic progestin promegestone (R5020), the location and characteristics of progestin receptors in the thymic cytosols from immature ovariectomized oestrogen-treated rats were determined. Tritiated promegestone bound to the cytosol with high affinity (dissociation constant (Kd) = 2.0 +/- 0.3 nmol/l; promegestone greater than progesterone greater than oestradiol greater than corticosterone testosterone) and low capacity (number of binding sites (Bmax) = 143.0 +/- 13.5 fmol/mg protein). These values were appropriate for progestin receptors. However, an extremely high dose of dexamethasone (10 mumol/l; 1000-fold excess over [3H]promegestone) slightly inhibited the specific binding. Progestin receptors were predominantly located in the reticuloepithelial (RE)-cell fraction, with few in the thymocyte T-cell fraction. The receptor level was raised (24.9 +/- 11.3 (S.E.M.) to 143.0 +/- 13.5 fmol/mg protein) with increased doses of oestrogen (0-30 micrograms) administered in vivo. Using sucrose density gradient ultracentrifugation it was found that the thymic progestin receptor had a sedimentation coefficient of 9S under low-salt conditions. These results clearly suggest that the thymus of the immature female rat contains a specific progestin receptor which is mainly located in the RE cells.