Temporal Changes in Activities of Enzymes Reducing Ring-A of Progesterone in the Fetus and Placenta of the Rat

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Abstract
The development of .DELTA.4-5.alpha.-reductase and 3.alpha.- and 3.beta.-hydroxysteroid dehydrogenases in rat fetuses and placentas was detected by the production of specific metabolites during in vitro incubation with progesterone. The metabolites, 5.alpha.-pregnane-3,20-dione, 3.alpha.-hydroxy-5.alpha.-pregnan-20-one, and 3.beta.-hydroxy-5.alpha.-pregnan-20-one, were identified by isolation and purification by TLC and reverse isotope dilution, followed by recrystallization of the free compound and a derivative. The .DELTA.4-5.alpha.-reductase and the 3.beta.-hydroxysteroid dehydrogenase are associated with the particulate fraction. However, 3.alpha.-hydroxysteroid dehydrogenase is a soluble enzyme present in the supernatant fraction of homogenized placentas and fetuses. The activities of these enzymes were greater in the placenta than in the fetus. As pregnancy progresses, the activities increase in the fetus, but diminish in the placenta. Although the placenta secretes only marginal amounts of progesterone, it has a notable capacity to metabolize progesterone to 5.alpha.-reduced metabolites. The fetus has the ability to utilize progesterone as early as day 13, and its potential to convert progesterone into ring-A reduced products increases during gestation.