Binding of estradiol-17 beta and estriol in cytosolic and nuclear fractions from urogenital tissues.

This report describes the measurement and partial characterization of the specific binding of estradiol (E2) and estriol (E3) in the cytosols and nuclear fractions from uterus, vagina, urethra and urinary bladder of the rabbit. Fractions from uterine and vaginal tissues showed the highest binding with both E2 and E3 approx 300 fmol/mg protein. The levels of specifically bound E3 were about 70% of the corresponding values for E2. In the sedimentation analysis the cytosolic receptors for both E2 and E3 exhibited 2 major forms, 3 S and 8 S, in addition to the heavy aggregates. Sephacryl S-200 chromatography showed major and minor components corresponding to mol. wt of 250.000 and 20.000-40.000 respectively. No noteworthy differences in the cytosolic receptors from different tissues could be observed in the above analyses. Whereas the uterine nuclear E2 receptor sedimented at 4.3 S the vaginal receptor distributed in two peaks, 2.5 S and 4.3 S. The receptor from both urethra and urinary bladder sedimented at 2.5 S. Nuclear E3 receptor, however, showed a major peak at 3.5 S in all cases. Some differences in tissue nuclear receptor were also observed in their chromatographic behaviour. The results confirm the existence of estrogen receptor in both urethra and urinary bladder, and the data of the limited physiochemical analysis indicate that the receptors in these tissues are essentially similar to those in the uterus or vagina.