STUDIES ON THE METABOLISM OF C-21 STEROIDS IN THE HUMAN FOETO-PLACENTAL UNIT

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Abstract
In situ perfusion of human mid-term placentas with labelled pregnenolone and 17[alpha]-hydroxypregnenolone was carried out. Following perfusion with pregnenolone in 2 experiments, 80 and 90% of the radioactive material recovered from the placenta and 15 and 29% of that recovered from the perfusate was progesterone. These figures accounted for 17 and 13% of the perfused dose. Perfusion with 17[alpha]-hydroxypregnenolone in 3 experiments indicated that 87, 66 and 73% of the radioactive material recovered from the placenta and 48, 44 and 52% of that found in the perfusates was 17 [alpha]-hydraxy-progesterone. These figures represent 26, 17 and 17% of the perfused material. Several polar metabolites of both pregnenolone and 17[alpha]-hydroxypregnenolone were also detected, but in amounts insufficient for their identification. It is suggested that conversion of circulating 3[beta]-hydroxy- [DELTA] 5-precursors into [alpha],[beta]-unsaturated 3-ketones may be a major pathway in the placental synthesis of progesterone and 17[alpha]-hydroxyprogesterone.