Androgen and Estrogen Receptors in the Canine Prostate

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Abstract
Characterization of cytosol and 0.6 M KCl‐nuclear androgen and estrogen receptors in the canine prostate is described, including methods for assay of these molecules in tissue samples from intact, adult dogs. Androgen receptors were quantitated by exchange incubations (20 hours for cytosol and 26 hours for nuclear extract at 0 C; incubations at higher temperatures (15 or 30 C) resulted in substantial reduction of saturable binding activity. Apparently, virtually all the estrogen receptor sites in cytosol and nuclear extract are unoccupied, since these were equally filled with H3‐estradiol at 0 C (nonexchange incubation) and 30 C (exchange conditions) during 20‐hour incubations. Androgen receptors were assayed using the synthetic androgen methyltrienolone (R1881), and estradiol‐17β was selected for estrogen receptor determinations. Using the assay conditions described, neither of these ligands bound to the sex steroid‐binding protein of canine blood. Steroid competition experiments indicated that the androgen and estrogen receptors are distinct molecules. Scatchard plot analyses were linear, suggesting a single class of high affinity sites for each receptor (Kd's in the 10−9 to 10−10 mol/l range). Saturable estradiol binding was additionally detected by sucrose gradient analysis of cytosol and nuclear extract. The 4S sedimentation of the cytosol receptor is typical of prostate cytoplasmic estrogen receptors; the nuclear form sedimented at 5S. The estrogen and androgen binding proteins satisfy criteria that distinguish them from blood steroid binding proteins and classify them as intracellular steroid hormone receptors.

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