Specificity of the acute tryptophan and tyrosine plus phenylalanine depletion and loading tests I. Review of biochemical aspects and poor specificity of current amino acid formulations

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

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

The acute tryptophan or tyrosine plus phenylalanine depletion and loading tests are powerful tools for studying the roles of serotonin, dopamine and noradrenaline in normal subjects and those with behavioural disorders. The current amino acid formulations for these tests, however, are associated with undesirable decreases in ratios of tryptophan or tyrosine plus phenylalanine to competing amino acids resulting in loss of specificity. This could confound biochemical and behavioural findings. Compositions of current formulations are reviewed, the biochemical principles underpinning the tests are revisited and examples of unintended changes in the above ratios and their impact on monoamine function and behaviour will be demonstrated from data in the literature. The presence of excessive amounts of the 3 branched-chain amino acids Leu, Ile and Val is responsible for these unintended decreases and the consequent loss of specificity. Strategies for enhancing the specificity of the different formulations are proposed.

Original languageEnglish (US)
Pages (from-to)23-34
Number of pages12
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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