Comparison of steroid concentrations in venous and arterial blood across the human testis. Unconjugated 5 alpha-androstane-3 beta, 17 beta-diol: an important androgen metabolite of the human testicular-epididymal unit.

By means of specific radioimmunoassays unconjugated testosterone, 5 alpha-dihydrotestosterone, 5 alpha-androstane-3 alpha, 17 beta-diol, 5 alpha-androstane-3 beta, 17 beta-diol and estradiol-17 beta as well as testosterone-glucosiduronate were estimated in the plasma of the spermatic vein and artery simultaneously with the determination in peripheral venous and arterial plasma in ten male patients undergoing orchiectomy for prostatic cancer. The following results were obtained: A positive concentration gradient was found for all steroids. The testicular "secretion" of 5 alpha-androstane-3 beta, 17 beta-diol was established for the first time. The venous-arterial transfer of the mentioned steroids within the plexus pampiniformis yielded the following figures: 5.1%; 17.4%; 6.5%; 5.4% 5.1% and 6.5%, respectively. The testicular and/or epididymal origin of the different steroids was calculated to be of the following order of magnitude (mean values): Dihydrotestosterone 28%, 5 alpha-androstane-3 alpha, 17 beta-diol 45%, 5 alpha-androstane-3 beta, 17 beta-diol about 100% estradiol-17 beta 63% and testosterone-glucosiduronate 3%.