Specificity of the acute tryptophan and tyrosine plus phenylalanine depletion and loading tests part II: Normalisation of the tryptophan and the tyrosine plus phenylalanine to competing amino acid ratios in a new control formulation

Abdulla A.B. Badawy, Donald M. Dougherty, Dawn M. Richard

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Current formulations for acute tryptophan (Trp) or tyrosine (Tyr) plus phenylalanine (Phe) depletion and loading cause undesirable decreases in ratios of Trp or Tyr + Phe to competing amino acids (CAA), thus undermining the specificities of these tests. Branched-chain amino acids (BCAA) cause these unintended decreases, and lowering their content in a new balanced control formulation in the present study led to normalization of all ratios. Four groups (n = 12 each) of adults each received one of four 50 g control formulations, with 0% (traditional), 20%, 30%, or 40% less of the BCAA. The free and total [Trp]/[CAA] and [Phe + Tyr]/[BCAA + Trp] ratios all decreased significantly during the first 5 h following the traditional formulation, but were fully normalized by the formulation containing 40% less of the BCAA. We recommend the latter as a balanced control formulation and propose adjustments in the depletion and loading formulations to enhance their specificities for 5-HT and the catecholamines.

Original languageEnglish (US)
Pages (from-to)35-47
Number of pages13
JournalInternational Journal of Tryptophan Research
Volume3
Issue number1
DOIs
StatePublished - 2010

Keywords

  • Acute tryptophan depletion and loading
  • Acute tyrosine depletion test
  • Amino acid formulations
  • Branched-chain amino acids
  • Catecholamines
  • Competing amino acids
  • Dopamine
  • Isoleucine
  • Leucine
  • Noradrenaline
  • Phenylalanine
  • Tryptophan
  • Tyrosine
  • Valine

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology

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