Transport and accumulation of alpha-aminoisobutyric acid (A.I.B.) in the guinea pig placenta.

Active transport of A.I.B. from mother to fetus was studied. This was done in the intact animal and using the isolated placenta, artificially perfused at both sides. It was shown that A.I.B. is actively accumulated in the placental cells. An estimate of the kinetic constants is given. It is shown that this accumulation takes place predominantly from the maternal side of the placenta. A.I.B. that has been accumulated is cleared to the maternal and fetal circulation in equal amounts. So the netto active transport from mother to fetus is brought about by an unequal distribution of carriers, the maternal side being most active.