title: Proline is synthesized from glutamate during intragastric infusion but not during intravenous infusion in neonatal piglets.
abstract: Glutamate is considered the primary precursor amino acid for proline synthesis in mammals. Evidence exists, however, suggesting that proline may be a dietary indispensable amino acid for 2.5-kg piglets due to inadequate synthesis. This hypothesis was tested by intravenous and intragastric infusion of radiolabeled amino acids in vivo. Piglets (3 to 4 d old) were surgically implanted with catheters in the femoral (infusion) and jugular (sampling) veins and in the stomach (feeding and infusion). Piglets were fed hourly, via the stomach catheter, a semi-purified diet containing 10% dried skim milk, 15% corn oil, amino acids, vitamins and minerals. Experiment 1 was a 2 X 2 factorial design, with 24 piglets adapted to either low or supplemental proline diets (1.3 and 16.4 g proline x kg(-1) respectively) for 7 d, then intravenously infused with either [U-14C]glutamate or [U-14C]proline (185 k Bq x kg(-1) prime; 370 kBq x kg(-1) x h(-1) constant) for 4 h. Experiment 2 followed similar protocols, with eight piglets adapted to the low proline diet for 7 d and [U-14C]glutamate or [U-14C]proline infused into the stomach catheter. Piglets infused intravenously with [U-14C]glutamate did not convert glutamate to proline. Radioactive label was recovered in proline in all of the piglets receiving intragastric infusion of [U-14C]-glutamate. The fractional synthesis rate of proline from intragastric glutamate was 125 microgram ol kg(-1) x h(-1), accounting for approximately 40% of the proline accumulated. These data provide conclusive evidence that intravenously infused glutamate is not used as a precursor for proline synthesis and that, although conversion of glutamate to proline occurs in the gastrointestinal tract, the rate is not sufficient to provide the proline accumulated.
authors.affiliation: Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.
authors.forename: J M
authors.initials: JM
authors.lastname: Murphy
authors.forename: S J
authors.initials: SJ
authors.lastname: Murch
authors.forename: R O
authors.initials: RO
authors.lastname: Ball
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001823:Body Composition; D002250:Carbon Radioisotopes; D004750:Enteral Nutrition; D018698:Glutamic Acid / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism*; D007262:Infusions, Intravenous; D007700:Kinetics; D011392:Proline / Q000008:administration & dosage* / Q000096:biosynthesis* / Q000097:blood; D013552:Swine / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; D018698:Glutamic Acid; D011392:Proline