5 Alpha-Reductase Inhibition by Finasteride (Proscar) in Epithelium and Stroma of Human Benign Prostatic Hyperplasia

Steroids. 1994 Nov;59(11):616-20. doi: 10.1016/0039-128x(94)90016-7.


Finasteride is a specific 5 alpha-reductase inhibitor that has been shown to reduce the size of human benign prostatic hyperplasia (BPH) by inhibiting the intraprostatic conversion of testosterone to 5 alpha-dihydrotestosterone. The aim of the present in vitro study was to describe in more detail the inhibitory effect of finasteride on 5 alpha-reductase in epithelium and stroma of human BPH. 5 alpha-Reductase activity in epithelium and stroma was inhibited dose-dependently by finasteride. The mean IC50 (50% inhibitory concentration) values, determined in the presence of various testosterone concentrations, were generally 2- to 4-fold lower in epithelium than in stroma. With finasteride concentrations greater than 5 nM, competitive inhibition of 5 alpha-reductase occurred both in epithelium and stroma. The mean inhibition constant Ki[nM +/- SEM] was 7 +/- 3 and 31 +/- 3 in epithelium and stroma, respectively. In the presence of finasteride concentrations < or = 5 nM, the epithelial 5 alpha-reductase seems to be inhibited in an uncompetitive manner, whereas such low finasteride concentrations cause either no inhibition (1-2 nM) or competitive inhibition (5 nM) in stroma. Our present study provides evidence that the inhibitory effect of finasteride on 5 alpha-reductase is much stronger in epithelium than in stroma. Therefore, it is conceivable that the global size-reduction of BPH under finasteride treatment is primarily due to the regression of BPH epithelium.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-alpha Reductase Inhibitors*
  • Aged
  • Aged, 80 and over
  • Epithelium / drug effects
  • Epithelium / enzymology
  • Finasteride / pharmacology*
  • Humans
  • Male
  • Middle Aged
  • Prostatic Hyperplasia / drug therapy
  • Prostatic Hyperplasia / enzymology*
  • Prostatic Hyperplasia / pathology
  • Stromal Cells / drug effects
  • Stromal Cells / enzymology


  • 5-alpha Reductase Inhibitors
  • Finasteride