Prostatic cytosol binding of 5α-androstane-3β,17β-diol and estradiol-17β

Abstract

The goal of the present research was characterization of the interaction of 5 α-androstane-3 β,17 β-diol(3 β-diol) with prostatic estradiol-17 β(E 2) binding sites to address the role of this 5 α-dihydrotestosterone(DHT) a metabolite in prostatic regulation. Using dextran-charcoal assay we demonstrated specific 3 β-diol and E 2 binding sites in rat ventral prostate cytosol (RVPC) and dog prostate cytosol (DPC). In both cytosols, E 2 binding is of high affinity (Ka⋍10 9 M −1; RVPC:68 fmol/mg protein, DPC:170 fmol/mg protein), and 3 β-diol binding is of moderate affinity (Ka⋍10 8 M −1; RVPC:62 fmol/mg protein, DPC:165 fmol/mg protein). Unlabeled 3 β-diol competes effectively for cytosolic 3H-E 2 binding sites, whereas unlabeled DHT, 5 α-androstane-3 α,17 β-diol (3 α-diol) and testosterone(T) are poor competitors for 3H-E 2 binding sites. Using DNA-cellulose column chromatography, we separated prostatic androgen and estrogen binding activities. The E 2 binding activity which adhered to DNA-cellulose was displaced by 100-fold excess 3 β-diol but not by DHT. Thus data from two assay procedures show competition of 3 β-diol for 3H-E 2 binding sites in rat and dog prostate.