Fetal bile salt metabolism: placental transfer of dihydroxy bile salts in sheep.

The bidirectional placental transfer of sodium [11,12-di-3H]chenodeoxycholate and sodium [14C]deoxycholate was studied in conscious pregnant sheep near term. In fetal-to-maternal studies, radiolabeled bile salt was injected into the fetal portal vein, and the daily excretion of radiolabel in maternal hepatic bile was measured over 3-4 days. In maternal-to-fetal studies, the mother received daily injections of radiolabeled bile salt, and the accumulation of label in the fetal pool was measured after 6-9 days. Bile salts were transferred predominantly as the taurine conjugate. Transfer rates were 1) fetus to mother; chenodeoxycholate, 6.7 mumol/24 h and deoxycholate, less than 0.5 mumol/24 h and deoxycholate, 1.4 mumol/24 h. We conclude that, in sheep near term, deoxycholate derived from the mother slowly accumulates in the fetus, while the placenta acts as an excretory route for fetal chenodeoxycholate.