title: Oral and intravenous tracer protocols of the indicator amino acid oxidation method provide the same estimate of the lysine requirement in healthy men.
abstract: To investigate whether splanchnic uptake of the indicator amino acid ([1-(13)C] phenylalanine) during the fed state alters the estimate of lysine requirement, five healthy men were studied at graded levels of lysine intake, with either an oral or intravenous (IV) tracer protocol, in a randomized, crossover design. Splanchnic extraction of the oral tracer was expressed as the difference between the ratio of the enrichments in urinary phenylalanine between tracer protocols. The rate of release of (13)CO(2) from (13)C-phenylalanine oxidation (F(13)CO(2)) was measured and a two-phase linear regression crossover model was applied to determine the lysine requirement. Mean splanchnic extraction of the oral tracer was approximately 19%. Although actual F(13)CO(2) was higher during oral tracer infusion (P < 0.001), the breakpoint was not different from that determined with IV infusion (P = 0.98), with both yielding a mean lysine requirement of 36.6 mg/(kg. d). The upper 95% confidence intervals were 52.5 and 53.3 mg/(kg. d) for the oral and IV isotope infusions, respectively. These results demonstrate that routes of isotope administration using the indicator amino acid oxidation technique do not affect the estimated amino acid requirement. Therefore, the indicator amino acid oxidation method using the oral route, which is less invasive and allows for studies in vulnerable groups such as infants and children, should be the preferred method for studying amino acid requirements.
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Canada M5S 3E2.
authors.forename: Wantanee
authors.initials: W
authors.lastname: Kriengsinyos
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Wykes
authors.forename: Ronald O
authors.initials: RO
authors.lastname: Ball
authors.forename: Paul B
authors.initials: PB
authors.lastname: Pencharz
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000601:Amino Acids, Essential / Q000008:administration & dosage* / Q000378:metabolism; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002247:Carbon Isotopes; D006801:Humans; D007275:Injections, Intravenous; D008239:Lysine / Q000008:administration & dosage* / Q000378:metabolism; D008297:Male; D009751:Nutritional Requirements; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000378:metabolism*; D012016:Reference Values
chemical_list: D000601:Amino Acids, Essential; D002247:Carbon Isotopes; D010649:Phenylalanine; D008239:Lysine