Specific high-affinity oestradiol binding in rat ventral prostate.

The presence of a specific saturable oestradiol-binding component was demonstrated in cytosol from rat ventral prostate. Centrifugation of cytosol, previously incubated with [3H]oestradiol at 0 degrees C, on low salt glycerol--Tris gradients revealed two oestradiol-binding systems with sedimentation coefficients of 8S and 4S. Excess unlabelled dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one) did not compete with the oestradiol binding, whereas excess unlabelled oestradiol or diethylstilboestrol abolished the 8S and 4S peaks. The oestradiol binding to these components could not be detected after proteolytic treatment. Scatchard analysis of saturable oestradiol binding in cytosol of prostates from intact rats and from rats 14 days after orchidectomy indicated that the equilibrium dissociation constant (KDeq) was about 10(-10) mol/l at 0 degrees C, and the concentrations of high-affinity binding sites were approximately 20 fmol oestradiol bound/mg protein. Lower concentrations of oestradiol binding (approximately 2 fmol/mg protein) were found in cytosols from prostates obtained 2 and 4 days after castration. The transient decrease of oestradiol binding was not due to the presence in prostate cytosol of a factor that inactivated the oestradiol receptor. It is proposed that the oestradiol receptor in the cytosol from ventral prostate tissue of the rat is under endocrine control.