title: Effects of mesenteric vein L-alanine infusion on liver metabolism of organic acids by beef heifers fed diets differing in forage: concentrate ratio.
abstract: Effects of diet forage:concentrate ratio and mesenteric vein L-alanine infusion on net VFA metabolism by portal-drained viscera (PDV) and liver were determined in four multicatheterized Hereford x Angus heifers (443 kg BW) fed in equal meals every 2 h pelleted, isonitrogenous diets containing 75% alfalfa or 75% corn:soybean meal (SBM) in a balanced single reversal of diets with 6 wk for adaptation. In addition, effects of L-alanine infusion on net metabolism of individual amino acids (AA) by PDV and liver was determined when heifers were fed 75% corn:SBM. Four measurements of blood flow (p-aminohippurate dilution) and net flux of VFA and AA (venous-arterial difference times blood flow) were obtained at 30-min intervals immediately before beginning and ending a 24-h mesenteric vein infusion of L-alanine at 75 mmol/h. Net PDV absorption of acetate (P < .02), propionate (P < .02), and total VFA (P < .02) was lower when 75% corn:SBM was fed, reflecting increased carbohydrate digestion postruminally and only partially balanced by increases in net PDV glucose absorption reported previously. In addition, net PDV absorption of n-butyrate was lower when 75% alfalfa was fed. Excluding acetate, net liver removal of VFA was 83 to 108% of their net PDV release. L-Alanine infusion did not affect net PDV or liver flux of VFA but decreased net total splanchnic (PDV plus liver) release of propionate (P < .07) and n-butyrate (P < .03) and decreased (P < .10) net PDV release and liver removal of glycine. In spite of the increase in liver L-alanine removal, the ratio of glucose release to precursor removal remained remarkably constant across the liver when L-alanine was infused, emphasizing the tight control of liver glucose release and the dynamic interplay of precursor supply and removal in the maintenance of liver carbon balance.
authors.affiliation: ARS, USDA, Beltsville, MD 20705.
authors.forename: C K
authors.initials: CK
authors.lastname: Reynolds
authors.forename: D L
authors.initials: DL
authors.lastname: Harmon
authors.forename: R L
authors.initials: RL
authors.lastname: Prior
authors.forename: H F
authors.initials: HF
authors.lastname: Tyrrell
mesh_terms: D000409:Alanine / Q000008:administration & dosage / Q000494:pharmacology*; D000596:Amino Acids / Q000378:metabolism*; D000821:Animal Feed / Q000592:standards; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004064:Digestive System / Q000098:blood supply / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000378:metabolism; D007262:Infusions, Intravenous / Q000662:veterinary; D008099:Liver / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D008642:Mesenteric Veins / Q000502:physiology; D010179:Pancreas / Q000098:blood supply / Q000378:metabolism; D012039:Regional Blood Flow / Q000187:drug effects; D013025:Glycine max / Q000592:standards; D013154:Spleen / Q000098:blood supply / Q000378:metabolism; D014508:Urea / Q000378:metabolism; D003313:Zea mays / Q000592:standards
chemical_list: D000596:Amino Acids; D005232:Fatty Acids, Volatile; D014508:Urea; D005947:Glucose; D000409:Alanine