Estrogen receptor and aromatase activity in the testes of the unilateral cryptorchid rat.

The intratesticular concentration of estradiol-17 beta (E2) is increased in the abdominal testis of rats made unilaterally cryptorchid at birth. To elucidate this observation testicular aromatase activity and testicular estrogen receptor concentration were studied. Aromatase activity was lower while the concentration of estrogen receptor was higher in the abdominal testis. Treatment of cryptorchid rats with the anti-estrogen Tamoxifen did not change testicular concentration of testosterone. However, Tamoxifen induced a significant reduction of E2 in the abdominal testis. The main factor responsible for the increased E2 concentration in the abdominal testis appears to be increased binding of estrogen.