Placental transfer of dexamethasone in near-term sheep.

The placental transfer of 3H-dexamethasone was studied in six near-term sheep. The placental clearance of 3H-dexamethasone was 18.8 +/- 3.5 ml/min per kg of fetal weight. The clearance of dexamethasone by the fetal tissues was 9.3 +/- w.5 ml/min per kg. The maximum placental clearance was 285 +/- 24 ml/min and the degree of diffusion limitation to the placental transfer of dexamethasone was 78 +/- 4%. The placental transfer of dexamethasone is therefore limited primarily by the nature of the placental barrier.