The conversion of cortisol into its principal metabolites, their tissular concentrations and transplacental transfer during 3H-cortisol infusion of mother and fetal guinea-pigs.

During continuous infusion of 3H-cortisol in the circulation of the guinea-pig mother or fetus, radioactive metabolites appear in both maternal and fetal blood. These cortisol-derived compounds were identified principally as cortisone, tetrahydrocortisol (THF) and tetrahydrocortisone (THE). There were unidentified others in low quantities. The cortisone of the maternal plasma is 100% maternal in origin since that of the fetal plasma is 50% fetal in origin between days 62 and 66 and increased thereafter. An identical profile was noted for THF. THE seemed to be synthetized in the fetal guinea-pig and was transferred to the mother in increasing amounts near term. Liver concentrations of cortisol were higher than those of plasma in the mother. Maternal liver appeared to be the main organ of cortisol metabolism in the mother-fetus unit, but maternal adrenal may contribute to this metabolism.