Abstract
Nuclear and cytoplasmic androgen receptors were identified in canine prostate preparations. Saturation analysis employing 5α-dihydrotestosterone and tissue from intact dogs demonstrated that crude nuclear pellets contained 85 femtomoles of KCI-extractable and 106 femtomoles of ethanol-extractable receptor sites per 100 μg DNA. The apparent 5α-dihydrotestosterone association constant, 3-3.5 × 108 M−1, and steroid binding specificity of both receptor fractions were identical. 5α-Dihydrotestosterone, 19-nortestosterone, 17β-testosterone, and 5α-androstane-3λ,17β-diol were effective inhibitors of the nuclear binding of radiolabeled 5α-dihydrotestosterone, whereas 5α-androstane-3α,17α-diol, δ4-androstene-3,17-dione, progesterone, estradiol, and cortisol were not. The sedimentation constant of the KCl-extractable nuclear receptor on linear sucrose gradients was 4-5S. Cytoplasmic saturation analysis, employing tissue obtained from dogs 72 hr post-orchiectomy, demonstrated that 5α-dihydrotestosterone and the synthetic androgen R 1881 (17β-hydroxy-17α-methyl-estra-4,9,11-trien-3-one) were bound to an identical number of receptor sites, 34.3 ± 5.9 femtomoles per mg cytosol protein, with apparent association constants of 0.73 ±0.06 × 109 M−1 and 1.9 ± 0.2 × 109 M−1 respectively. Receptor binding of radiolabeled R 1881, measured at 2°, was readily inhibited by 5α-dihydrotestosterone and 19-nortestosterone; was modestly inhibited by 5α-androstane-3α,17β-diol, estradiol, and progesterone, and was not affected by δ4-androstene-3,17-dione, 5α-androstane-3α,17α-diol or cortisol. Estradiol and progesterone inhibition of R 1881 binding was markedly diminished at 15°, whereas androgen inhibition of R 1881 binding was temperature invariant. The sedimentation constant of the cytoplasmic R 1881- or 5α-dihydrotestosterone-receptor complex was 9-10S on linear sucrose gradients. The canine prostate nuclear and cytoplasmic androgen receptors had properties similar to those of the respective rat ventral prostate androgen receptors.