BINDING OF 3H-OESTRADIOL WITH RECEPTORS IN THE HUMAN ENDOMETRIUM AND MYOMETRIUM

Abstract

ABSTRACT The in vivo and in vitro binding of 3H-oestradiol-17β to cytoplasmic and nuclear fractions of the human endometrium and myometrium was demonstrated by different techniques. Sucrose density gradient ultracentrifugation of the endometrial cytoplasm showed that oestradiol binds with two specific proteins sedimenting at 8.5 S and 5.1 S. Myometrial cytoplasmic oestrogen binding protein (OeBP) had a sedimentation coefficient of 5.1 S. Nuclear OeBP in the endometrium and myometrium had the same sedimentation value of 4.2 S. The endometrial cytoplasmic OeBP separated by gel chromatography showed association with both oestradiol and oestrone in the ratio of 2:1. The OeBP in nuclear fraction of the endometrium and myometrium showed binding with oestradiol and oestrone in the ratio of 2.5:1 and 2:1 respectively. The association of oestrone along with oestradiol with receptors of the endometrial and myometrial nuclear and cytoplasmic fractions suggests that oestrone may play a significant role in the overall action of oestrogens in the human uterus. Studies on ligand specificity of the OeBPs showed that oestrone which is a comparatively weaker oestrogen, competitively displaced bound 3H-oestradiol, more or less in a similar way as a highly potent oestrogen diethylstilboestrol (DOeS). Chlormadinone acetate (CAP), among the progestational steroids tested, maximally displaced bound oestradiol. The significance of these findings in the mechanism of action of oestradiol in the human uterus is discussed.