Net metabolism of plasma amino acids by liver and portal-drained viscera of fed sheep
Wolff, J.E.; Bergman, E.N.; Williams, H.H.
American Journal of Physiology 223(2): 438-446
1972
ISSN/ISBN: 0002-9513 PMID: 5046759 Document Number: 55244
Net appearance in portal plasma and net hepatic metabolism of amino acids were estimated from measurements of plasma flow and venoarterial concentration differences in 10 experiments on sheep fed on 800 g/day of lucerne pellets containing 20% crude protein. Most amino acids were added to portal plasma in highly significant quantities except that net additions of aspartate and glutamate were extremely small while glutamine was utilized by gut tissue (1.5 mmoles/h). The liver removed most of the amino acids added to portal plasma. Large hepatic uptakes of glycine, alanine and glutamine (2 to 4 mmoles/h) and to a less extent serine, tyrosine, arginine and phenylalanine were noted, and this must have accompanied a net release from peripheral tissues. Valine, isoleucine and leucine uptake by the liver was generally less than their gut output. Glutamate and ornithine were always produced by the liver. Ammonia production by the portal-drained viscera (12.2 g N/day) was 65% of the total N added to the portal blood or 48% of the intake. All was removed by the liver. The data thus emphasize the wastage of protein in the ruminant on a high-protein diet and also that, due to metabolism in gut tissues and liver, net splanchnic output of each amino acid is different from its rate of absorption.