Transepithelial movement of 3H-androgen in rat seminiferous and caput epididymal tubules: saturability and effect of competition with estradiol.

Proluminal movement of 3H-testosterone from peritubular space to intratubular fluids of the adult rat testis and epididymis was studied by using in vivo microperfusion and subsequent micropuncture of seminiferous tubules and caput epididymal tubules. Tubules were perifused with Minimum Essential Medium containing 3H-testosterone. To determine if androgen transport is saturable, 40, 80, 160, and 320 microCi 3H-testosterone were included in the perfusion fluid. Radioactivity of 3H-androgens in the intraluminal fluids was determined at 1 hour after perfusion. Transepithelial 3H-androgen movement in the testis was linear (r = 0.735, p < 0.001, y = 0.17 x +5.6). The movement of 3H-androgen across the epididymal epithelium was saturable (Vmax of 326.5 nM/hr and Km of 77 nM). To determine the effect of estradiol on proluminal androgen movement, estradiol at 10X the cocentration of 3H-testosterone was incorporated in the perifusion fluid. Proluminal 3H-androgen movement into the seminiferous and epididymal tubules was not affected by addition of estradiol to the perifusion fluid. These findings support our previous observations that proluminal transepithelial movement of 3H-androgens could be mediated by its binding to a specific intraluminal androgen binding protein.