17 beta-hydroxysteroid oxidoreductase in epithelium and stroma of human prostate.

It is conceivable that androstenedione contributes indirectly to 5 alpha-dihydrotestosterone formation in human prostate by its intraprostatic conversion to testosterone. This reversible conversion is catalyzed by the enzyme 17 beta-hydroxysteroid oxidoreductase (17 beta-HSOR). At present, rather limited information on kinetic parameters like specific concentration (Vmax), affinity to steroid substrates (KmS) and to pyridine nucleotides (KmN) of 17 beta-HSOR is available. Thus, we determined those aforementioned kinetic parameters in epithelium and stroma of normal human prostate (NPR) and benign prostatic hyperplasia (BPH). The main results were: (1) the mean KmS of 17 beta-HSORred/NADPH was significantly (P < 0.0001) lower than those of all other 17 beta-HSORs. (2) In almost all cases the mean Vmax was higher in BPH than NPR. (3) In all cases, the mean Vmax/KmS ratios of 17 beta-HSORred were higher than those of 17 beta-HSORox. The highest ratio was found regarding 17 beta-HSORred/NADPH in BPH stroma. (4) In stroma, a significantly positive correlation of Vmax/KmS of 17 beta-HSORred/NADPH with age was found. (5) The lowest KmN was found regarding NADP+, followed by NADPH. It is concluded that in human prostate the balance of the reversible conversion of testosterone to androstenedione is shifted potentially towards testosterone, particularly in BPH stroma.