Possible mechanism of induction of benign prostatic hyperplasia by estradiol and dihydrotestosterone in dogs.

A mechanism of induction of canine benign prostatic hyperplasia (BPH) by androgen-stimulated growth of prostatic cells exposed to estrogen-induced toxicity. Estrogen is thought to be activated by redox cycling of catechol metabolites, a mechanism of generation of active radicals. Mongrel dogs, 4 animals/group, were sham-operated (controls) or were treated for 60 days with implants of 5 alpha-dihydrotestosterone and/or estradiol-17 beta. The activities of drug and hormone metabolizing enzymes (aryl hydrocarbon hydroxylase, 7-ethoxycoumarin O-deethylase, and estradiol-17 beta-2- and -4-hydroxylase) in prostate were significantly elevated by chronic treatment with either estradiol-17 beta or 5 alpha-dihydrotestosterone plus estradiol-17 beta, but not in kidney or liver which are not targets of hormone-induced hyperplasia. Activities of the detoxifying enzymes catalase and glutathione peroxidase I in prostate were increased by estradiol-17 beta treatment, whereas in kidney or liver they were not affected or changed to a lesser degree than observed in prostate. Free radial-induced damage (carbonyl content) of proteins was observed in prostate of dogs treated with either estradiol-17 beta or 5 alpha-dihydrotestosterone plus estradiol-17 beta and in liver protein by treatment with either 5 alpha-dihydrotestosterone or 5 alpha-dihydrotestosterone plus estradiol-17 beta. It was concluded that the patterns of estradiol-17 beta- or 5 alpha-dihydrotestosterone plus estradiol-17 beta-induced increases in activities of catechol estrogen synthase and of other drug metabolizing enzymes were consistent with the postulated free radical generation by redox cycling of catechol estrogen specifically in the prostate. The increases in activities of detoxifying enzymes may represent an (albeit insufficient) response to prostatic free radical damage to protein in prostate is consistent with a postulated induction of BPH via injury by estrogen metabolites followed by 5 alpha-dihydrotestosterone-stimulated growth of altered prostatic cells.