Estradiol and progesterone binding components in the cytosol of normal human fallopian tubes

The in vitro binding of labeled estradiol and R5020 to receptor proteins from human fallopian tube cytoplasmic fractions has been studied. Both compounds give rise to two separate peaks in density gradient analysis experiments under low ionic strength conditions: a "8 S" steroid-hormone-specific peak and a "4 S" peak accounted for by non-specific binding. The receptor molecules were further characterized by a competition studies, electrophoretic technique and gel chromatography. The receptor content for both steroid hormones varied throughout the menstrual cycle. The estradiol and progesterone receptor concentration were highest during the proliferative phase and were very significantly lower in the second half of the menstrual cycle. Furthermore measurement of both receptors in the cytosol revealed differences among the anatomical segments of the fallopian tube. The highest estradiol and progesterone binding could be detected in the ampullary region, significantly lower levels of estradiol and progesterone receptor were seen in the infundibulum and the isthmus.