Amino acid metabolism in the isolated perfused rat liver.

1. Rat livers have been perfused with homologous blood and the distribution of (15)N from labelled amino acids added to the perfusate studied.2. Each of the amino acids added, aspartate, alanine, glycine, and glutamate (unlabelled) were rapidly removed from the perfusate. Glutamate was formed from added aspartate (but not from added alanine or glycine) by transamination in the perfusate plasma; the perfusate concentration of no other amino acid was affected by addition of any of the acids investigated.3. Urea output was increased by addition of aspartate, increase in output after addition of alanine or glycine was not significant.4. After addition of labelled aspartate, alanine or glycine an increase in isotope ratio was detected in urea, ammonia, glutamine, aspartate and alanine in the perfusate and, in some experiments, in the liver. After addition of alanine an increase was also detected in lysine, tyrosine, phenylalanine, methionine, proline, tryptophan and threonine+serine (analysed together).