Placental transfer of aromatic amino acids in non-human primates.

Macaca fascicularis (crab-eating monkeys) underwent an operative procedure at 120 to 130 days of pregnancy that allowed fetal blood sampling. During subsequent experiments L-phenylalanine and p-chlorophenylalanine were injected into the maternal circulation. Blood obtained from mother and fetus revealed that phenylalanine is actively transported across the placenta and hence is markedly increased in the fetus if the maternal blood phenylalanine concentration is below the "saturation" level of 1.82 mM to 2.12 mM. The results of these studies which provide a better understanding of placental transport mechanisms of aromatic amino acids will be of assistance in future management of pregnant phenylketonuric females.