Assessment of the androgen environment within the human testis: Minimally invasive method to obtain intratesticular fluid

Previous studies of the rat have shown that testosterone concentrations wit hin the interstitial and seminiferous tubular fluids of the testes are sign ificantly higher than normal serum levels, and further, that although intra testicular testosterone concentration can be substantially reduced without an effect on spermatogenesis, the concentration that is minimally required to maintain spermatogenesis is also substantially higher than serum levels. The purpose of the present study was to adapt a minimally invasive techniq ue to sample human intratesticular fluid to enable parallel observations in man. To this end, aspiration methods were first developed for the rat test is and then adapted to the human. The testosterone concentration in fluid o btained by unilateral aspiration of rat testes was approximately 50 ng/mL, similar to the known concentration in seminiferous tubular fluid, These asp iration methods were then adapted to obtain intratesticular fluid from huma n testes. Studies of 12 fertile human subjects demonstrated that percutaneo us testicular aspiration could be performed safely and successfully using a 19-gauge needle. Nine additional human subjects had bilateral testicular a spiration and simultaneous measurement of peripheral blood testosterone lev els. Testicular aspirations yielded 8 to 117 muL Of fluid from each testicl e. The mean concentration of testosterone in aspirates obtained from the 21 patients was 609 +/- 50 ng/mL. Dihydrotestosterone and 3 alpha -androstane diol concentrations were quite low, below the limits of detection of our as say. The SHBG/ABP concentration in the aspirates was 8.5 +/- 1.1 nM. These results define testosterone as the major androgenic steroid in the human te stis, as in the rat testis, and indicate that the testosterone concentratio n within the human testis is approximately 200-fold greater than that of SH BG/ABP, and more than 100-fold greater than the concentration of testostero ne found in normal human serum.