THE ANDROGEN RECEPTOR OF THE UROGENITAL TRACT OF THE FETAL-RAT IS REGULATED BY ANDROGEN

To provide insight into androgen-mediated virilization, we measured th e androgen receptor in tissues of male and female rat fetuses prior to and during the period of phenotypic sex differentiation. Western immu noblotting was performed utilizing an antibody directed against the 21 amino-terminal segment of the androgen receptor. In immunoblots prepa red from urogenital tract tissues of day 17 male and female fetal rats , this antibody specifically recognizes a 110K protein band characteri stic of the androgen receptor. Androgen receptor levels were low to un detectable in a variety of non-urogenital tract tissues. After day 18 of fetal development, the amount of androgen receptor decreased in fem ale urogenital tissues, and by day 22 the amount of immunoreactive and rogen receptor was higher in the male urogenital sinus and tubercle th an in the corresponding tissues of the female. Administration of 5 alp ha-dihydrotestosterone to pregnant rats at a dose of 50 mg/kg body wei ght per day from day 12 to day 22 caused an increase in immunoreactive androgen receptor in the female urogenital sinus and tubercle to leve ls approaching those in male tissues. Administration of the androgen a ntagonist flutamide (100 mg/kg body weight per day) during the same in terval caused a reduction in androgen receptor level in the urogenital sinus and tubercle of the male. These findings suggest that androgens modulate the amount of androgen receptor in the embryonic urogenital tract either by inducing the proliferation of androgen-responsive cell s or by increasing androgen receptor levels in individual cells.