title: Amino acid supplementation does not alter whole-body phenylalanine kinetics in Arabian geldings.
abstract: Stable isotope infusion methods have not been extensively used in horses to study protein metabolism. The objectives were to develop infusion and sampling methodologies for [1-(13)C] phenylalanine and apply these methods to determine whether the addition of supplemental amino acids to a control diet affected whole-body phenylalanine kinetics in mature horses. Arabian geldings were studied using a 6-h primed (9 μmol/kg), constant (6 μmol · kg(-1) · h(-1)) i.v. infusion of L-[1-(13)C] phenylalanine, with blood and breath sampled every 30 min, to measure whole-body phenylalanine kinetics in response to receiving the control diet (n = 12) or the control diet supplemented with equimolar amounts of glutamate (+Glu; 55 mg · kg(-1) · d(-1); n = 5), leucine (+Leu; 49 mg · kg(-1) · d(-1); n = 5), lysine (+Lys; 55 mg · kg(-1) · d(-1); n = 5), or phenylalanine (+Phe; 62 mg · kg(-1) · d(-1); n = 6). The plasma concentrations of the supplemented amino acid in horses receiving the +Leu, +Lys, and +Phe diets were 58, 53, and 36% greater, respectively, than for the control treatment (P < 0.05). Isotopic plateau was attained in blood [1-(13)C] phenylalanine and breath (13)CO(2) enrichments by 60 and 270 min, respectively. Phenylalanine flux (+20%) and oxidation (+110%) were greater (P < 0.05) in horses receiving the +Phe treatment than in those fed the control diet. There was no effect of treatment diet on nonoxidative phenylalanine disposal or phenylalanine release from protein breakdown. The developed methods are a valuable way to study protein metabolism and assess dietary amino acid adequacy in horses and will provide a useful tool for studying amino acid requirements in the future.
authors.affiliation: Department of Animal and Poultry Science, Virginia Tech, Blacksburg, VA, USA. klur222@uky.edu
authors.forename: Kristine L
authors.initials: KL
authors.lastname: Urschel
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Geor
authors.forename: Mark D
authors.initials: MD
authors.lastname: Hanigan
authors.forename: Pat A
authors.initials: PA
authors.lastname: Harris
mesh_terms: D000596:Amino Acids / Q000008:administration & dosage*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002247:Carbon Isotopes; D019587:Dietary Supplements; D018698:Glutamic Acid / Q000008:administration & dosage; D006736:Horses / Q000097:blood / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000008:administration & dosage; D008239:Lysine / Q000008:administration & dosage; D008297:Male; D009751:Nutritional Requirements; D009919:Orchiectomy; D010649:Phenylalanine / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D018698:Glutamic Acid; D010649:Phenylalanine; D007930:Leucine; D008239:Lysine