Distribution of testosterone and 5alpha-dihydrotestosterone in rat epididymis and their concentrations in efferent duct fluid.

5alpha-Dihydrotestosterone concentrations were found to be appreciably higher in the proximal portion of the rat epididymis than in the distal portion. Following ligation of the efferent ducts of a testis, the 5alpha-dihydrotestosterone concentration diminished in the proximal half but not in the distal half of the epididymis. Epididymal fluid and spermatozoa were washed out from minces of epididymal tissue. The numbers of spermatozoa present in the wash fluid and in the homogenate of washed minces of epididymal tissue were used as measures for the amounts of epididymal fluid present in these fractions. Of the total amount of 5alpha-dihydrotestosterone (30-2 ng/g tissue) in the proximal portion, 20-5 ng were localized in the epididymal fluid, whereas of the total amount of 5alpha-dihydrotestosterone (8-6 ng/g tissue) in the distal portion, 2-8 ng were found in the epididymal fluid. The amounts of testosterone present in the fluids of both proximal and distal portions were 1-2 ng/g tissue. In contrast to the epididymal fluid, efferent duct fluid had a high concentration of testosterone (28-8 ng/ml) and a low concentration of 5alpha-dihydrotestosterone (1-9 ng/ml). These data suggest that the fluid surrounding the spermatozoa in the testis and the epididymis contains a high concentration of androgen and that as the fluid moves from the testis to the epididymis there is a clear change in the ratio of testosterone to 5alpha-dihydrotestosterone.