Abstract

In vivo androgen kinetics were determined in six young (21--49 yr) and elderly men (62-77 yr) with prostatge hyperplasia (BPH). Steady-state infusions of [14C]testosterone and [3H]androstanediol (3 alpha diol) were given, which allowed determination of the conversions testosterone leads to dihydrotesterone (DHT) in equilibrium or formed from 3 alpha diol. These infusions also yield metabolic clearance data which, together with meaurement of nonisotopic steroid levels, yield estimations of blood production rates. The production rate for testosterone was 6.04 +/- 1.66 vs. 3.69 +/- 0.62 mg/d, whereas the production rate for 3 alpha diol was 319 +/- 57 and 193 +/- 34 micrograms/d (P < 0.05 both groups). The irreversible conversion rate of testosterone to DHT was 3.1 +/- 0.4 and 3.5 +/- 0.9% (NS). The back conversion of 3 alpha diol to dHT was high (68 +/- 25 vs. 81 +/- 17, NS) indicating that 3 alpha diol might cause BPH as a result of conversion to DHT in vivo. The conversion of DHT to 3 alpha diol is reduced in the elderly group (15.8 +/- 2.6 and 6.3 +/- 1.4, P < 0.001). Since DHT formation in the prostate is a key event in the development of BPH and blood DHT appears to be a measure of extrasplanchnic sexual target tissue activity, our in vivo studies suggest that the tissue increase in DHT may result from reduced metabolism and the activity of 3 alpha-oxidoreduction favors the oxidative pathway in elderly men.