Estrogen and progesterone receptors in human uterus and oviduct

The binding of 3H-estradiol and 3H-R5020 (dimethyl-19-norpregna-4,9-diene-3,20-dione) to estrogen (ER) and progesterone (PR) receptors in human uterus and oviduct were studied. The binding of the ligands to their respective receptors were of high specificity and affinity. The equilibrium dissociation constants for ER and PR were 0.07 +/- 0.025 nM respective 0.76 +/- 0.22 nM in the oviduct and 0.065 +/- 0.015 nM respective 0.82 +/- 0.25 nM in the uterus (mean +/- SE) (n = 12). Sucrose density gradient centrifugation revealed in both tissues specific binding in the area sedimenting at 8 S whereas the slower sedimenting 4 S and 5 S peaks contained both specific and non-specific binding. The oviductal cytosol contained a similar proteolytical activity that has been described in human uterine and breast cancer tissue. The protease, which can be inhibited by diisopropylfluorophosphate, converts the 8 S receptor from into a 4.2 S proteolytic fragment. The KCl-extracted uterine and oviductal estrogen and progesterone receptors sedimented at 5.2 S in both low salt (0.01 M KCl) and high salt (0.4 M KCl) sucrose gradients. It is well known that the suppression of the estrogen receptor system by progesterone correlates with suppressed function in the oviduct but with increased growth and secretory activity in the uterus. In the light of the present data it is concluded, that the difference in the hormonal response in the two tissues is most likely not due to differences in the binding characteristics of the estrogen or progesterone receptors.