The extrasplanchnic origin of blood dihydrotestosterone in elderly men

The splanchnic extraction and interconversion of testosterone (T) and dihydrotestosterone (DHT) were studied in 5 elderly men undergoing cardiac catheterization using a constant infusion of [1,2-3H] testosterone and [4-14C] DHT. Metabolic clearance rate (MCR), splanchnic extraction (SE), splanchnic clearance (SC), extrasplanchnic clearance (ESC), transfer constant in blood ([p] T-DHT BB) and transfer constant across the liver ([p] T-DHT SB) were calculated. The MCRT was 675 +/- 108 (mean +/- SC) L/day and MCRDHT was 409 +/- 68 L/day. SET was 45.9 +/- 7.0% and SEDHT was 18.5 +/- 5.4%. When these values are compared with those recently reported by us for normal men, there is a 1/3 reduction in SET and 1/2 reduction for SEDHT in elderly men. The calculated SCT and ESCT were 355 +/- 72 L/day and 320 +/- 86 L/day, respectively. SCDHT and ESCDHT were 145 +/- 48 L/day and 263 +/- 77 L/day respectively, suggesting that a major fraction of DHT is metabolized in extrasplanchnic organs. No evidence for a net appearance of DHT by either mass or specific activity analysis in hepatic vein blood was observed indicating that the splanchnic compartment does not contribute DHT into the circulation either by de novo synthesis or via conversion from testosterone. This work indicates that conversion of testosterone to DHT in elderly men occurs entirely in extrasplanchnic tissue.