UNEQUAL BINDING OF ESTROGENS IN HUMAN-ENDOMETRIUM

The binding characteristics of estradiol-17β (E2), estrone (E1), estriol (E3) and 17α-ethynylestradiol-17β (EE2) in the cytosol fraction of human endometrium have been studied. An unequal binding for the different estrogens was observed: a similar number of binding sites (RE2) are able to bind E2 and EE2 with high affinity (5.9-7.7 × 109 M-1), E3 with a lower affinity (1.6 × 109M-1). A different number of binding sites (RE1 are able to bind E1 with high affinity (5.3 × 109M-1). The proportion RE1/RE2 is variable during the menstrual cycle, increasing during the luteal phase. Progesterone may be one of the regulatory factors of this variation. © 1979.