Absence of 5 alpha-reductase activity in the gubernaculum during descent of the fetal pig testis.

To evaluate the hypothesis that testicular descent is mediated by the action of high local concentrations of dihydrotestosterone in the gubernaculum, testis, or epididymis, we obtained tissues from 30 male pig fetuses between 63 and 101 days of gestation. We assayed the 5 alpha-reductase activity in homogenates of pooled tissue by following the conversion of (3H)testosterone to (3H)dihydrotestosterone. The 5 alpha-reductase activity in the urethra and prostate increased prior to and during, but decreased after, the period of testicular descent. The 5 alpha-reductase activity in the gubernaculum remained constant throughout gestation and was not significantly higher than the background activity found in umbilical cord, testis plus epididymis, striated thigh muscle and heat inactivated samples of prostate and urethra. Prior to testicular descent, the 5 alpha-reductase activity was approximately 60 to 300 times higher in the urethra than in the gubernaculum, and approximately 20 to 55 times higher in the prostate than in the gubernaculum. These findings indicate that local conversion of testosterone to dihydrotestosterone in the gubernaculum or epididymis does not play a role in the mediation of testicular descent in the pig fetus.