Demonstration of Androgen-Binding Components in Rat Epididymis Cytosol and Comparison with Binding Components in Prostate and Other Tissues1

Abstract

Rat epididymis cytosol, labeled by incubation with dihydrotestosterone-l,2-3H at 0 C or by injection of testosterone-l,2-3H sc, contained 2 androgen-binding components, one of which demonstrated a high affinity for dihydrotestosterone. The mean constant of dissociation (Kd) of the high affinity component was 7.0 × 109M as determined by methods of dextrancoated charcoal adsorption, sucrose gradient ultracentrifugation and Sephadex gel equilibrium. When epididymis cytosol labeled with dihydrotestosterone-l,2-3H, in amounts which are bound largely by the high affinity binding component, was fractionated by sucrose gradient ultracentrifugation, the radioactivity migrated in a single peak with sedimentation coefficient of 4S in comparison with the 3.5S and 8S peaks of prostate cytosol. Acrylamide gel electrophoresis of similarly labeled epididymis cytosols revealed 2 peaks of radioactivity, while prostate contained only a single peak corresponding to the slower moving epididymis peak. Rat serum and cytosols of submandibular gland, kidney and muscle contained 3–4S binding components on sucrose gradients, but on acrylamide gels none formed peaks of radioactivity corresponding to those of epididymis. Rat serum, likewise, demonstrated no specific binding affinity for dihydrotestosterone by Sephadex gel equilibrium. The binding affinity for dihydrotestosterone was determined by displacement assays to be approximately twice that for testosterone and 17β-estradiol, and much greater than the affinities for 5α-androstane-3α,17β-diol or androstenedione. These studies indicate that rat epididymis cytosol contains a specific binding component with high affinity for dihydrotestosterone and with physical properties different from the androgen-binding components of prostate cytosol. (Endocrinology89: 143, 1971)