PROGESTERONE METABOLISM BY HUMAN FETAL AND PLACENTAL TISSUES: INTERCONVERSION OF PROGESTERONE AND 20α-HYDROXYPREGN-4-EN-3-ONE IN THE FETO-PLACENTAL UNIT IN VITRO

Abstract

The metabolism of progesterone in the feto-placental unit in vitro was studied. Homogenates of four fetal livers (after 22-28 weeks gestation) were incubated with progesterone-4-¹⁴C with an NADPH generating system, and a large amount of 20α-hydroxypregn-4-en-3-one and smaller amounts of 5β-Apregnane-3α-o1-20-one and 5β-pregnane-3α, 20α-diol were identified. It is therefore considered that the major pathway of progesterone metabolism was: progesterone→20α-hydroxypregn-4-en-3-one, and that the activity of Δ4-3-keto steroid hydrogenase in fetal liver was significantly lower than after birth. The conversion of 20α-hydroxypregn-4-en-3-one to progesterone was shown to take place in vitro in a homogenate of human placenta with added NADP. These results suggest that the interconversion of progesterone and 20α-hydroxypregn-4-en-3-one occurs in the feto-placental unit, permitting the reutilization of progesterone which is indispensable for maintenance of pregnancy.