AMINO ACID METABOLISM DURING FETAL DEVELOPMENT

ABSTRACT

Fetal and placental amino acid metabolism has been studied using multiple tracer methodology. Comparisons between species have been difficult because of technical differences that make such comparisons inappropriate. However, comparisons of the metabolism of different amino acids within the same species, the fetal lamb, are now possible because of the abundance of studies carried out in this species. The role of placental metabolism in contributing to the determination of the supply of amino acids to the fetus has been better defined. Some amino acids such as glutamate are catabolized significantly within the placenta, others are transported with little placental catabolism. The organ specificity noted in adult metabolism for specific amino acids is now well established in fetal life as well. Fetal hepatic metabolism is characterized by a large uptake of most amino acids and by a net release of glutamate and serine. Amino acid uptake by the hindlimb differs significantly from postnatal life not only in the magnitude of the amino acid uptake but also by the fact that amino acids normally released from the hindlimb in postnatal life such as alanine and glutamine are taken up by these tissues in fetal life. The impact of changes in the fetal biologic state introduced by hypoxia or by undernutrition are just beginning to be investigated in terms of the flux of amino acids to protein synthesis versus catabolism and oxidation.