| RESEARCH PAPER
|Year : 1999 | Volume
| Issue : 2 | Page : 120-123
Effects of finasteride and epristeride on steroid 5a-reductase kinetics-A comparative in vitro study
Zu-Yue Sun, Hong Xie, zeng-Hong Tu
Objective: To compare the effect of finasteride with that of epristeride on 5(-reductase kinetics in vitro to explain the increase in serum testosterone level by finasteride but not by epristeride when treated for benign prostatic hyperplasia.
Methods: Sprague-Dawley rat liver microsomal crude suspension served as the source of steroid ?(?-reductase. The enzyme, Tris-HCl buffer, [3H] testosterone and epristeride or finasteride were incubated together at 37oC for 20 min. The substrate, [3H] testosterone, and its product, [3H] dihydrotestosterone (DHT) were isolated by thin-layer chromatography. To measure the initial velocity of [3H] DHT (the activity of 5(-reductase), the radioactivity of [3H] DHT, scrapped off thin-layer plate was determined with isotope scintillation counter. The enzyme activity was expressed as (M/min of [3H] DHT.
Results: Epristeride was an uncompetitive inhibitor, but finasteride was a competitive one to steroid 5(- reductase and their inhibition constants were 67 ( 19 and 25 ( 3 nM, respectively.
Conclusion: The inhibition mechanism of finasteride different from epristeride perhaps was the reason for increase in serum testosterone levels in patients with benign prostatic hyperplasia treated by finasteride.
Source of Support: None, Conflict of Interest: None