BIOSYNTHESIS OF PROGESTERONE FROM ENDOGENOUS STEROID PRECURSOR BY THE GUINEA-PIG PLACENTA

Summary. The supernatant resulting from centrifugation of a homo-genate of the central portion of the guinea-pig placenta at 1000 g was found to synthesize progesterone from endogenous precursor. Addition of an NAD- or NADPH-generating system stimulated progesterone production. Placental steroidogenesis in the guinea-pig is of special interest because this animal shares with the human the ability to maintain pregnancy if ovariecto-mized during the latter half of gestation. This observation indicates that the guinea-pig placenta synthesizes progesterone. Heap & Deanesly (1966) found that the plasma progesterone concentration was correlated with placental weight in the ovariectomized guinea-pig. They also reported a fivefold higher progesterone level in the plasma after passage through the uterus. However, Ferguson & Christie (1967), using histochemical methods, were unable to detect-3/í-hydroxysteroid dehydrogenase in the guinea-pig placenta during the latter portion of gestation. Recently, Bedwani & Marley (1971) were able to show conversion of exogenous pregnenolone to progesterone by guinea-pi