Stromal 5 alpha-reductase activity is elevated in benign prostatic hyperplasia.

The activities of 5 alpha-reductase and 3 alpha (beta)-hydroxysteroid dehydrogenase were assayed in homogenates of stroma and epithelium obtained from 3 normal, 9 hyperplastic and 2 carcinomatous human prostates. Irrespective of the normal or abnormal condition of the prostate, the localization of 5 alpha-reductase was predominantly in stroma whereas the reductive and oxidative activities of 3 alpha (beta)-hydroxysteroid dehydrogenase were more evenly divided between stroma and epithelium. Furthermore, the mean specific activity of 5 alpha-reductase in hyperplastic stroma at 84.6 plus or minus 13.1 (plus or minus SEM) pmol 30 min-1 mg protein-1 was almost 3 times greater (Student's t-test, P < 0.05) than the corresponding value in normal stroma, 31.6 plus or minus 7.2 pmol mg protein-1 30 min-1. We conclude that the stroma is the primary site of conversion of testosterone to dihydrotestosterone in the human prostate owing to the prevalence in stroma of 5 alpha-reductase, and that benign prostatic hyperplasia is characterized by an increased amount of stromal 5 alpha-reductase activity.