Changes in placental enzymatic activities in relation to estrogen production during pregnancy

: To study the mechanism of production of estrogen during pregnancy, the following in vitro and in vivo studies were undertaken; 1) Weight of human placenta and total estradiol (E2) levels in the maternal peripheral vein were measured at different weeks of gestation. 2) Changes in E2 levels after DHA-S 100mg loading were calculated at the 1st, 2nd and 3rd trimesters. 3) Steroid enzyme activities including sulfatase, 3 beta-HSD and aromatase in placenta obtained in the 1st, 2nd and 3rd trimesters were measured. Results were as follows; 1) The weight of the human placenta increased gradually as gestation progressed. Twofold placental weight was noticed from the 2nd to the 3rd trimester. 2) Total E2 in the maternal peripheral vein increased steadily, being 4.07 +/- 1.74 ng/ml at the 1st trimester, 27.72 +/- 11.67 ng/ml and 104.12 +/- 57.89 ng/ml at the 2nd and 3rd trimesters respectively. The increase in E2 from the 2nd to the 3rd trimester was greater than that of the placental weight. 3) Increases in E2 following DHA-S loading were 1.01 ng/ml at the 1st, 29.2 ng/ml at the 2nd and 98.2 ng/ml at the 3rd trimester. 4) No significant differences were observed between placental 3 beta-HSD and sulfatase activities in the placenta obtained at the three different stages of pregnancy, while aromatase activity was found to be significantly higher in the placenta of the 3rd trimester than that of 2nd trimester. These results indicate that the remarkable increase in estrogen production in the 3rd trimester may be explained partially by increased aromatizing enzyme activity in the placenta.