Properties of the estrogen receptor in the human oviduct and its interaction with ethinylestradiol and mestranol in vitro.

Abstract

Biochemical properties of estrogen binding are investigated in the cytosol and nuclear fractions of the human Fallopian tube. Sucrose density ultracentrifugation and dextrancoated charcoal adsorption techniques are used for characterization of [3H]estradiol uptake in the human oviduct. There is indirect evidence for the presence of protease which can be inhibited by diisopropylfluorophosphate (DFP). When DFP is present in buffer of low ionic strength, the cytosol receptor sediments at 8S and 4S peaks. In the absence of DFP, the 4S peak alone is demonstrated. The proteolytic inhibitor does not alter the estrogen-binding capacity in the human oviduct. The dissociation constant (Kd) for [3H]estradiol in cytosol is 2 X 10(-10) M without DFP and 1.5 X 10(-10) M with DFP. The presence of protease in cytosol of human oviducts is confirmed by hydrolysis of benzoyl-arginine nitroanalide. The enzymatic activity is inhibited by DFP. Nuclear estrogen receptor sediments at 4S after extraction with 0.4 M KCL buffer. A rapid nuclear accumulation of [-3H]estradiol is seen at 25 C, with reciprocal depletion of cytoplasmic receptor in human oviduct tissue minces. The synthetic estrogens ethinylestradiol (17 alpha-ethynyl-1,3,5-estratriene-3,17 beta-diol) and mestranol [3-methoxy-17 alpha-ethinyl-1,3-5(10)-estratiene-17 beta-OL] are competitors for the estrogen receptor in the human Fallopian tube. Inhibition of oviductal estrogen binding is 500 times greater with ethinylestradiol than with mestranol (ki = 0.75 X 10(-9) M for ethinylestradiol; Ki = 3.74 X 10(-7) M for mestranol). The estrogen receptor in the human Fallopian tube shows properties similar to those of the estrogen receptor of the human uterus. However, the determination of the number of binding sites in the oviduct is not influenced by proteolytic enzyme activity.