Estradiol Receptors in the Urethra and the Bladder of the Female Rabbit

The presence of estradiol receptors was investigated in urethral and bladder tissue of mature pregnant and nonpregnant rabbits. Cytosolic fraction and nuclei were incubated with tritiated estradiol (3H-E2) at concentrations from 1 nM to 20 nM at 30 degrees C for 3 h with or without a 100-fold excess of diethylstilbestrol (DES). Incubation at 30 degrees C was selected so as to measure both occupied and unoccupied binding sites. The number of binding sites and their association constants were calculated by Scatchard analysis. Cytosolic binding sites for estradiol with high affinity (Ka = 0.31-0.58 X 10(9) M-1) were found in urethral tissue (785 fmol/mg DNA) and in bladder tissue (771 fmol/mg DNA). These results suggest that lower urinary tract of female rabbit could be a target organ for estradiol.