Effects of Glucagon on Amino Acid Transport and Utilization in the Perfused Rat Liver

The effects of glucagon on the output of amino acids by the isolated rat liver perfused with recirculating medium were to decrease that of glycine, glutamate, and phenylalanine; to increase greatly that of leucine, isoleucine, valine, and tyrosine; and to increase slightly that of lysine and histidine. In livers perfused with nonrecirculating medium containing amino acids at concentrations found in plasma from normal rats, glucagon produced changes in intracellular and extracellular concentrations which suggested a stimulation of (a) intracellular utilization of glycine, alanine, glutamate, and phenylalanine; (b) intracellular production of leucine, isoleucine, and valine; and (c) inward transport of lysine and, in other experiments, the nonmetabolizable amino acids, α-aminoisobutyrate and 1-aminocyclopentane carboxylic acid. The changes in amino acid concentrations caused by glucagon resembled those found in diabetic animals.