ON THE PERMEABILITY OF THE GUINEA PIG PLACENTA TO INTRAVENOUSLY INJECTED PROGESTERONE-4-14C

The permeability of the guinea pig placenta to progesterone was studied by injecting progesterone-4-14C intravenously into seven pregnant guinea pigs, and determining the levels of radioactivity in the plasma samples taken from the mothers and foetuses during 15 minutes after the injection. The ratio of the levels of radioactivity in the plasma of the foetus to the level in the plasma of the mother increased with time. In three experiments progesterone-4-14C was injected into the umbilical vein of one of the foetuses in the uterus. Radioactivity was measured in the plasma samples that were taken from the mother from 2 to 23 minutes after the injection. A low level of radioactivity was also found in some of the plasma samples taken from the other foetuses. These observations show that radioactive progesterone or its metabolites pass through the guinea pig placenta in both directions.