In vitro metabolism of prednisolone, dexamethasone, betamethasone, and cortisol by the human placenta.

Many of the factors influencing the pharmacologic action of corticosteroids on the maternal-placental-fetal unit remains obscure. To clarify the effect of the placenta on corticoid transfer, tritiated steroids were incubated in saline for 2 hours with minces of midgestational or term placental tissue. The media were extracted and chromatographed on Sephadex-LH-20. Large peaks corresponding to the inactive 11-keto metabolites were observed for cortisol (67 per cent) and prednisolone (51 per cent) while conversion of dexamethasone (1.8 per cent) and betamethasone (7.1 per cent) was low or negligible.