Hormonally Responsive Areas of the Reproductive System of the Male Guinea Pig. III. Presence of Cytoplasmic Estrogen Receptors

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Abstract
The administration of estrogens to intact adult male guinea pigs resulted in a variety of morphological changes in their accessory sex organs (the seminal vesicles, prostate, common ejaculatory chamber, coagulating gland and epididymis). To ascertain if a biochemical basis existed for a direct action of estrogens on these tissues, they were examined for the presence of estrogen receptors. Cytosol prepared from the accessory sex glands contains a macromolecular binding component for estradiol-17.beta.. This component sediments as an 8S species on 5-20% sucrose gradients under low (0.01 M KCl) ionic strength conditions and as a 4S species under high (0.4 M KCl) ionic strength conditions. Time-course studies indicate that binding equilibrium is achieved in .apprx. 2 h; dissociation of [3H]estradiol from the binding protein is very slow (t1/2 > 42 h). The cytoplasmic binder is highly specific for estrogens; the relative affinities of various estrogens for the protein were estradiol = 1, estrone = 0.72, diethylstilbestrol = 0.30 and estriol = 0.17. Progesterone, testosterone and 5.alpha.-dihydrotestosterone, even at a 1000-fold excess, caused < 10% inhibition of [3H]estradiol binding to the protein. The binder present in cytosol prepared from the accessory sex organs (excluding the epididymis) exhibited an equilibrium dissociation constant of .apprx. 0.3 nM, and there were .apprx. 30 f[femto]moles of binding sites/mg of cytosol protein. The cytoplasmic estrogen binder exhibits the characteristics usually attributed to receptors and is clearly different from a 4S, nonspecific, rapidly dissociating binder that is present in plasma. On the basis of steroid specificity, the cytoplasmic estrogen binder is distinct from the androgen receptor that is present in male reproductive tissues.