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Using whole‐body phenylalanine kinetics to measure the effects of amino acid supplementation in mature horses
Author(s) -
Urschel Kristine L.,
Geor Raymond J.,
Wagner Ashley L.,
Williamson Lindsey M.,
Smith Tracy L.,
Hanigan Mark D.,
Harris Pat A.
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.927.9
Subject(s) - phenylalanine , amino acid , kinetics , leucine , chemistry , bicarbonate , lysine , zoology , medicine , biochemistry , endocrinology , biology , physics , quantum mechanics
Stable isotopes have not been used in horses to measure whole‐body protein kinetics or to assess the adequacy of a diet's amino acid profile. The objective of this study was to determine whether supplementing a control diet (CON) with equal (0.38 mmol/kg/d) amounts of either glutamate (+GLU), leucine (+LEU), lysine (+LYS) or phenylalanine (+PHE) would affect whole‐body PHE kinetics in mature horses. 12 mature male horses were each studied 3 times: once while receiving the CON diet (n=12) and while receiving 2 of the 4 supplemented diets (n=6/diet). Following 7d of adaptation, horses received two 6h primed, constant infusions each period: [1‐ 13 C]PHE (d8) and [ 13 C]bicarbonate (d9). Breath samples were collected to measure the rate of 13 CO 2 appearance, to calculate PHE oxidation (d8) and total CO 2 production (d9). Blood was sampled (d8) to calculate PHE flux and kinetics using a stochastic model. Horses receiving the +LEU, +LYS and +PHE diets had higher plasma concentrations of their supplemented amino acid than when they received the CON diet (P < 0.05). Relative to CON, horses receiving +PHE had a greater PHE flux (+20%) and rate of PHE oxidation (+111%) (P < 0.05). There were no differences in PHE use for protein synthesis relative to CON for any of the supplemented diets (P > 0.05). The isotope methodology was sensitive enough to detect differences in PHE oxidation between diets. Amino acid supplementation of the CON diet did not appear to increase whole‐body protein synthesis in mature horses. Funded by WALTHAM Centre for Pet Nutrition.