Different mechanisms are involved in 3H-androgen uptake by the rat seminiferous and epididymal tubules in vivo.

Proluminal movement of 3H-androgen from peritubular to intratubular fluids of the adult rat testis and epididymis was investigated by using in vivo microperifusion and subsequent micropuncture of seminiferous tubules and caput, corpus, and cauda epididymal tubules. Tubules were perifused with Minimum Essential Medium containing 3H-testosterone. 14C-polyethyleneglycol was included in the perifusion fluid as a marker for contamination of intraluminal fluid by peritubular fluid. Radioactivity of isotopes in interstitial and intraluminal fluids was determined at 1 and 2 hours after perifusion and the percentage of peritubular isotopes appearing in the intraluminal fluid was determined. Proluminal movement of 3H-androgen across the seminiferous epithelium was significantly restricted. In contrast, intraluminal 3H-androgen concentrations in the caput epididymal fluid were 200-300% of those in the peritubular fluid at both 1 and 2 hours after perifusion. Similar results were found in the corpus epididymis. 3H-androgen concentrations in the cauda epididymal fluid were approximately 125% of the peritubular isotope concentrations. The exact mechanism underlying this uphill transepithelial movement of 3H-androgen in the rat epididymis continues to be elucidated.