Differences in the effects of estradiol on dihydrotestosterone induced prostatic growth of the castrate dog and rat.

The treatment of castrate beagles with a combination of estradiol an dihydrotestosterone (DHT) results in the synergistic enhancement of prostatic growth and the experimental induction of benign prostatic hyperplasia. This estradiol synergism can be shown as a greater than 3 fold increase in both prostatic wet weight and total DNA content in castrate dogs treated with both steroids, as compared to those animals treated with DHT alone. In direct contrast to the situation in the dog, there was no evidence of estradiol synergism on prostatic growth when castrate rats were treated with combinations of estradiol and DHT, even if both the ratio and absolute amount of both steroids were experimentally varied over a wide range of values. Regardless of the ratio or absolute dose, estradiol was completely unable to synergize the DHT induced growth of the prostate as well as other sex accessory tissues of the castrate rat. This indicates a fundamental difference between the rat and dog in regard to prostatic growth response to combinations of estradiol and DHT treatment.