A specific cytosolic estrogen receptor in human term placenta

Abstract

Administration of the antiestrogen ethamoxytriphetol (MER-25) during baboon gestation results in a marked decline in placental progesterone production. Since this effect in primates may be modulated via an estrogen receptor, the present study investigated the possible existence of an estrogen receptor in human placenta. Villous tissue of human, term placentas was homogenized in 0.01M Tris-HCl, ethylenediaminetetraacetic acid, dithiothreitol, glycerol buffer. Cytosol was incubated with 10−8M [3H] 17β-estradiol (E2) in the presence or absence of 10−6M diethylstilbestrol (DES). A single peak of [3H]E2 binding occurred in the 5.2 region after glycerol density gradient centrifugation, which was competed for by DES, E2, and enclomiphene. Scatchard analysis demonstrated E2 binding, which was saturable, of high affinity (Kd = 1.90 × 10−11M) and of low capacity (N = 0.13 × 10−14 moles/mg cytosolic protein). Competition for [3H]E2 binding was DES > E2 > estrone > MER-25 > enclomiphene, whereas androgens, progestins, and corticosteroids were ineffective. The results fulfill the criteria for a specific estrogen receptor. The influence of antiestrogen and, possibly, estrogen upon placental function in baboons may be modulated by an estrogen receptor.