Liver nitrogen movements during short-term infusion of high levels of ammonia into the mesenteric vein of sheep.
Four 40 kg wethers were used in a crossover design to quantify, by arterio-venous procedures, the mass transfer of NH3, urea and amino acids (AAs) across the portal-drained viscera and the liver during a 31 min infusion of either 0 (C0) or 1100 (C1100) micromol NH4HCO3/min into the mesenteric vein. In C1100, hepatic NH3 extraction remained stable at 1214 micromol/min (1.90 micromol/min per g wet liver weight), the capacity for hepatic NH3 removal was exceeded by 654 micromol/min and the incremental (C1100-C0) urea-N release: NH3 -N removal ratio increased progressively, from 0.52 to 0.90. The NH4HCO3 infusion reduced total branched-chain AA transfer across the portal-drained viscera and total AA-N and lysine extraction by the liver. Hepatic release of glutamate was augmented ornithine switched from net release to net removal and net splanchnic release of free essential AA (44 micromol/min (sed 9.2), ) and branched-chain AA (33 micromol/min (sed 2.0), ) were reduced to 0.58 of their basal rate. The study showed that conversion of excess NH3 to urea during a short-term hepatic NH3 overload required no additional contribution of AA-N to ureagenesis; essential AA and branched-chain AA supply to non-splanchnic tissues was, however, temporarily decreased.
Milano
G D
GD
Facultad de Ciencias Veterinarias, Universidad Nacional del Centro, Campus Universitario (7000) Tandil, Argentina. gmilano@vet.unicen.edu.ar
Lobley
G E
GE
D000596:Amino Acids / Q000378:metabolism; D000597:Amino Acids, Branched-Chain / Q000378:metabolism; D000641:Ammonia / Q000008:administration & dosage* / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001692:Biological Transport; D018592:Cross-Over Studies; D018698:Glutamic Acid / Q000378:metabolism; D007262:Infusions, Intravenous; D008099:Liver / Q000378:metabolism*; D008297:Male; D008642:Mesenteric Veins; D009584:Nitrogen / Q000378:metabolism*; D009952:Ornithine / Q000378:metabolism; D012756:Sheep; D013997:Time Factors; D014508:Urea / Q000378:metabolism*
D000596:Amino Acids; D000597:Amino Acids, Branched-Chain; D018698:Glutamic Acid; D000641:Ammonia; D014508:Urea; D009952:Ornithine; D009584:Nitrogen