title: Interactions between ruminal degradable nitrogen intake and in vitro addition of substrates on patterns of amino acid metabolism in isolated ovine hepatocytes.
abstract: The effects of ammonia (as NH4Cl) and propionate on the partitioning of amino acids between oxidation and gluconeogenesis were determined in isolated hepatocytes obtained from sheep fed a basal diet (50:50 bromegrass hay:corn; asfed basis) with or without urea. Hepatocyte suspensions were incubated with NH4Cl (0, 1.25, 2.5 and 5.0 mmol/L) and/or propionate (0, 2.5 and 5.0 mmol/L), in the presence of either 2.5 mmol/L L-alanine and 18.5 kBq L-[1-14C]alanine or 2.5 mmol/L L-glutamate and 18.5 kBq L-[1-14C]glutamate. Increasing the level of ruminal degradable nitrogen with urea increased in vitro rates of oxidation to 14CO2 of [1-14C]alanine, but not [1-14C]glutamate. Increasing in vitro concentrations of NH4Cl and propionate between 0 and 5 mmol/L reduced the rates of oxidation to 14CO2 of both [1-14C]alanine and [1-14C]glutamate. Synthesis of [14C]glucose with [1-14C]alanine, but not [1-14C]glutamate as the substrate, was increased 100% by feeding urea. Increasing in vitro levels of NH4Cl between 0 and 5 mmol/L reduced the rates of conversion of [1-14C]alanine and [1-14C]glutamate to [14C]glucose in hepatocytes isolated from sheep fed both diets. Increasing in vitro levels of propionate between 0 and 2.5 mmol/L elevated production rates of [14C]glucose from both radiotracers, but from 2.5 to 5.0 mmol/L propionate no further increase was evident. Feeding urea increased in vitro rates of urea nitrogen production. Increasing propionate levels between 0 and 5 mmol/L reduced ureagenic rates in liver cells isolated from sheep fed both diets. Oxygen (O2) uptake was unaffected by diet and NH4Cl; however, increasing propionate between 0 and 5 mmol/L increased rates of O2 uptake. It is concluded that in isolated sheep hepatocytes, detoxification of excessive ammonia may cause a repartitioning of alanine and glutamate metabolism towards oxidation and gluconeogenesis.
authors.affiliation: Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Mutsvangwa
authors.forename: J G
authors.initials: JG
authors.lastname: Buchanan-Smith
authors.forename: B W
authors.initials: BW
authors.lastname: McBride
mesh_terms: D000409:Alanine / Q000032:analysis / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000641:Ammonia / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001806:Blood Urea Nitrogen; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D005260:Female; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism; D008099:Liver / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D011422:Propionates / Q000378:metabolism / Q000494:pharmacology; D012417:Rumen / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism* / Q000502:physiology
chemical_list: D000596:Amino Acids; D002250:Carbon Radioisotopes; D011422:Propionates; D018698:Glutamic Acid; D000641:Ammonia; D005947:Glucose; C029658:propionic acid; D009584:Nitrogen; D000409:Alanine