Testosterone and dihydrotestosterone concentrations in plasma, epididymal tissues, and seminal fluid of adult rats.

The concentration of testosterone (T) and 5alpha-dihydrotestosterone (DHT) in plasma, seminal fluid, and epididymis of male Wistar rats have been determined by radioimmunoassay. The DHT/T ratio rose from 0.1 in blood to 1 in testicular fluid and 4 in epididymal fluid. This ratio is 2 in tissues of "caput" epididymis and 1 in "cauda" epididymis. These data indicate a transformation of T to DHT in the epididymal tissue, particularly at the "caput" level.