L-tyrosine fails to potentiate several peripheral actions of the sympathomimetics

Pharmacol Biochem Behav. 1991 Jul;39(3):755-9. doi: 10.1016/0091-3057(91)90159-y.


We have recently reported the ability of L-tyrosine (L-TYR) to potentiate the anorectic activity of various mixed-acting sympathomimetics including phenylpropanolamine (PPA), l-ephedrine (EPH) and d-amphetamine (AMP). Included in those studies was the attenuation of L-TYR's effect when coadministered with L-valine, a large neutral amino acid which competes with L-TYR for uptake into the brain, suggesting a central locus for the action of L-TYR. To determine to what extent L-TYR can potentiate peripheral actions, we investigated the effects of L-TYR with either PPA (20 mg/kg), EPH (20 mg/kg) or AMP (1.75 mg/kg) on gastric transit, gastric retention and intrascapular brown adipose tissue thermogenesis. In each of the paradigms studied, PPA, EPH and AMP significantly increased the expected sympathomimetic-mediated response, but no potentiation of L-TYR was observed. These results are consistent with the hypothesis that L-TYR potentiates the anorectic activity of the mixed-acting sympathomimetics largely via an action at a central locus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipose Tissue, Brown / drug effects
  • Animals
  • Appetite Depressants / pharmacology*
  • Body Temperature Regulation / drug effects
  • Dextroamphetamine / pharmacology
  • Drug Synergism
  • Ephedrine / pharmacology
  • Gastrointestinal Transit / drug effects
  • Male
  • Peripheral Nerves / drug effects*
  • Phenylpropanolamine / pharmacology
  • Rats
  • Rats, Inbred Strains
  • Stomach / drug effects
  • Sympathomimetics / pharmacology*
  • Tyrosine / pharmacology*
  • Valine / pharmacology


  • Appetite Depressants
  • Sympathomimetics
  • Phenylpropanolamine
  • Tyrosine
  • Ephedrine
  • Valine
  • Dextroamphetamine