title: Integrative physiology of splanchnic glutamine and ammonium metabolism.
abstract: The substrates for hepatic ureagenesis are equimolar amounts of ammonium and aspartate. The study design mimics conditions in which the liver receives more NH(+)(4) than aspartate precursors (very low-protein diet). Fasted dogs, fitted acutely with transhepatic catheters, were infused with a tracer amount of (15)NH(4)Cl. From arteriovenous differences, the major NH(+)(4) precursor for hepatic ureagenesis was via deamidation of glutamine in the portal drainage system (rather than in the liver), because there was a 1:1 stoichiometry between glutamine disappearance and NH(+)(4) appearance, and the amide (but not the amine) nitrogen of glutamine supplied the (15)N added to the portal venous NH(+)(4) pool. The liver extracted all this NH(+)(4) from glutamine deamidation plus an additional amount in a single pass, suggesting that there was an activator of hepatic ureagenesis. The other major source of nitrogen extracted by the liver was [(14)N]alanine. Because alanine was not produced in the portal venous system, we speculate that it was derived ultimately from proteins in peripheral tissues.
authors.affiliation: Department of Nutrition, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: D
authors.initials: D
authors.lastname: Yang
authors.forename: J W
authors.initials: JW
authors.lastname: Hazey
authors.forename: F
authors.initials: F
authors.lastname: David
authors.forename: J
authors.initials: J
authors.lastname: Singh
authors.forename: R
authors.initials: R
authors.lastname: Rivchum
authors.forename: J M
authors.initials: JM
authors.lastname: Streem
authors.forename: M L
authors.initials: ML
authors.lastname: Halperin
authors.forename: H
authors.initials: H
authors.lastname: Brunengraber
mesh_terms: D000136:Acid-Base Equilibrium; D000818:Animals; D001158:Arteries; D001769:Blood / Q000378:metabolism; D004285:Dogs; D005973:Glutamine / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism / Q000652:urine; D009587:Nitrogen Isotopes; D011169:Portal Vein; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D005973:Glutamine; D009584:Nitrogen