Effect of hormone injections on levels of cytosolic receptors for estrogen, androgen and progesterone in dog prostate.

We have studied the effects of estradiol injections on cytosolic estrogen, androgen and progesterone receptor levels in order to understand the role of this steroid in the induction of prostatic hyperplasia in the dog. Adult mongrel dogs were castrated and were then given injections of estradiol (0.25, 0.8 or 2.5 mg) dissolved in olive oil containing 5% benzyl alcohol on days 0, 2, 5 and 7 after castration. Steroid receptor levels were determined by Scatchard analysis using charcoal assay one day after the last injection. All three receptors were increased maximally with the 0.8 mg dosage when compared with castrated controls. Estradiol binding increased from 89 +/- 10 (mean +/- SEM) to 361 +/- 37 fmol per mg prot., androgen binding from 47 +/- 5 to 123 +/- 11 fmol per mg prot. and progesterone binding from 26 +/- 3 to 211 +/- 36 fmol per mg prot. The small dose of estradiol. (0.25 mg) produced a significant (P less than 0.05) increase of the progesterone receptor levels from 25 +/- 3 to 48 +/- 14 fmol/mg prot. Substitution of estradiol by 5 alpha-androstan-3 beta,17 beta-diol (2.5 or 25 mg) resulted in receptor levels similar to castrated animals. However treatment with 5 alpha-androstan-3 alpha,17 beta-diol (25 mg) alone or in combination with estradiol (0.25 mg) increased significantly the androgen receptor while it decreased the estrogen receptor. These results show that the administration of estradiol at doses used to induce experimental prostate hyperplasia produce measurable effects in the prostate and suggest that the estradiol receptor may be implicated in this phenomenon.