title: Source and amount of dietary nonspecific nitrogen in relation to whole-body leucine, phenylalanine, and tyrosine kinetics in young men.
abstract: We studied the effects of amount and source of nonspecific nitrogen (NSN) on the oxidation of leucine and hydroxylation of phenylalanine. In phase 1, seven adult males received for 6 d diets providing indispensable amino acid intakes to meet the 1985 FAO/WHO/UNU (FAO) requirements or our proposed requirement values (MIT). During one diet period with each diet, the NSN of the basal diets (total nitrogen intake: 107 mg N.kg-1.d-1) was increased to a total of 160 mg N.kg-1.d-1. On the morning of day 7, an 8-h constant intravenous tracer-infusion protocol (3-h fast; 5-h fed state) was conducted with L-[1-13C]leucine, L-[ring-2H5]phenylalanine, and L-[3,3,2H2]-tyrosine as tracers. In phase 2, six subjects were given three diets for 6 d, supplying 107 mg N.kg-1.d-1; NSN was a mixture of dispensable amino acids in which glutamine accounted for 0%, 12.5%, and 100% of total NSN. Leucine oxidation and phenylalanine hydroxylation rates and whole-body leucine and phenylalanine balances were unaffected by addition of supplemental NSN to the diets in phase 1 or by amino acid source of NSN in phase 2. Leucine and phenylalanine balances were lower (P < 0.05) for FAO compared with MIT diets.
authors.affiliation: Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge 02139.
authors.forename: T
authors.initials: T
authors.lastname: Hiramatsu
authors.forename: J
authors.initials: J
authors.lastname: Cortiella
authors.forename: J S
authors.initials: JS
authors.lastname: Marchini
authors.forename: T E
authors.initials: TE
authors.lastname: Chapman
authors.forename: V R
authors.initials: VR
authors.lastname: Young
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000097:blood; D002245:Carbon Dioxide / Q000378:metabolism; D004032:Diet; D006801:Humans; D007930:Leucine / Q000378:metabolism / Q000493:pharmacokinetics*; D008297:Male; D008954:Models, Biological; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism / Q000493:pharmacokinetics*; D012119:Respiration; D014443:Tyrosine / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D000596:Amino Acids; D002245:Carbon Dioxide; D014443:Tyrosine; D010649:Phenylalanine; D007930:Leucine; D009584:Nitrogen