Investigation of Precursor Availability in the Regulation of Estrogen Synthesis in Normal Human Pregnancy

To assess the influence of precursor availability on estrogen synthesis in normal human pregnancy, dehydroepiandrosterone sulfate (DHAS) (0 to 200 mg) was given intraamniotically to 9 volunteers in late gestation. Serum 17β-estradiol (SE2), total estriol (SE2), human chorionic gonadotropin (HCG), human chorionic somatomammotropin (HCS) and total urinary estrogens (UE) were measured before and after injection. Increases in SE2 were significant at all doses, while changes in UE and SE3 were not marked until 100 mg or more DHAS was given. It is concluded that precursor availability has a dominant role in regulating estrogen synthesis in normal pregnancy. The lack of significant change in HCG or HCS levels when serum estrogens were elevated suggests absence of a feedback mechanism between these hormones.