ESTRADIOL AND PROGESTERONE RECEPTORS IN DOG PROSTATE CYTOSOL

When intact or castrated dog prostate cytosol is incubated with tritiated estradiol, high levels of saturable binding can be observed in the 3-4S region of sucrose gradients. Occasionally a shoulder is also seen in the 8S region. The estradiol binding is specific for natural and synthetic estrogens. It is of high affinity (KA = 2 × 109M-1). The binding component also has a relatively high affinity for 5α-androstane-3β,17β-diol, a major metabolite of 5α-dihydrotestosterone in dog prostate cytosol. Estradiol and 5α-androstane-3β,17β-diol can displace each other in competition experiments and they both yield identical concentration of sites by Scatchard analysis. The concentration of estradiol binding sites is quite variable in prostates from 24 h castrated dogs and no apparent correlation can be found between the concentration of sites and prostate wt. By contrast in the prostates from intact dogs there is a highly significant inverse relationship between prostate wt. and concentration of estradiol binding sites. The presence of progesterone receptors in dog prostate can also be demonstrated by sucrose density gradient analysis using the synthetic steroids R5020 (17,21-dimethyl-19-norpregna-4,9-diene-3,20-dione) and R1881 (17β-hydroxy-17α-methyl-estra-4,9,11-trien-3-one). The binding component sediments both in the 8S and 4S regions of sucrose gradients. It is present in low amounts under basal conditions. Five days after a single injection of estradiol valerate, the binding is increased about 10-fold. It is almost completely abolished by the addition of progesterone and various unlabeled synthetic progestins but only partly decreased by 5α-dihydrotestosterone. Relatively low and constant levels of progesterone receptors are observed in normal and hyperplastic prostates from adult dogs (30 ± 1 [S.E.M.] fmol/mg0. prot.). © 1979.