PARENT SESSION
Pregnancy and Parturition

ESTROGENS, SEX STEROID BINDING PROTEIN (SBP) AND ESTROGEN RECEPTORS (ER / ER) IN THE HUMAN TERM FETAL-PLACENTAL VASCULAR SYSTEM.

Benassayag, Claudine¹, Mondon, Françoise¹, Robert, Brigitte¹, Mignot, Thérèse-Marie¹, Ferré, Françoise¹, ¹

ABSTRACT- There is compelling evidence that steroid hormones produced in large amounts during pregnancy play a central role in modulating growth, differentiation and function of the fetal-placental unit. However, the effect of estrogens, especially through estrogen-protein interactions in fetal-placental circulation, is still unclear. This study included women undergoing elective caesarean section at term (n=15). 17-Estradiol (E₂) and estrone (E₁) were measured by RIA, and their specific carrier plasma binding protein, SBP, was measured by immunoquantitation in fetal-placental circulation [umbilical arteries (A) and veins (V)]. Data from A and V were compared with the maternal intervillous (I) and peripheral (M) circulations. Finally, the presence of estrogen receptors throughout the fetal-placental vascular tree was investigated. Plasma E₂ concentrations were significantly lower in A (42nM), V (49nM ) and I (68nM) than in M (106nM) (p<0.001). E₁ levels were lower in A (23nM), V (35nM) and M (31nM) than in I (147nM) (p<0.001). Plasma SBP levels were 9- to 12-fold lower in umbilical cord blood (27nM for A and 26nM for V) than in I (233nM) or M (339nM) (p<0.001), leading to an E₂/SBP ratio in A, V, I and M of 1.5, 2.1, 0.3 and 0.4 respectively. RT-PCR analysis showed expression of ER and ER> mRNAs in the wall of placental stem villi vessels, chorionic arteries and veins, umbilical arteries and veins. Binding kinetics revealed a single class of high affinity binding sites for E₂ in cytosolic extract of all placental vessels, with Kd values in the range of 0.4-0.6 nM and a number of binding sites of 150 to 240 fmoles/mg protein. In conclusion, the high E₂/SBP ratio found in fetal-placental circulation indicates greater E₂ avaibility for estrogen receptors present in the fetal-placental vessels, and suggests estrogen mediated control of fetal-placental blood flow.

KEY WORDS: Human, Placenta, Estrogen receptors, Sex steroid binding protein