Effects of L-tyrosine on mixed-acting sympathomimetic-induced pressor actions

Pharmacol Biochem Behav. 1992 Dec;43(4):1047-52. doi: 10.1016/0091-3057(92)90479-y.


We previously reported the ability of L-tyrosine (L-TYR) to potentiate the anorectic activity of various mixed-acting sympathomimetics including [R*S*]-(+/-)-norephedrine [phenylpropanolamine (PPA)], [1R,2S]-(-)-ephedrine (EPH), and [S]-(+)-amphetamine (AMPH) in hyperphagic rats. Included in those studies was the attenuation of L-TYR's effect when coadministered with L-valine, a large neutral amino acid that competes with L-TYR for uptake into the brain, suggesting a central locus for the action of L-TYR. Additional studies demonstrated the inability of L-TYR to alter the peripherally mediated PPA-, EPH-, and AMPH-induced increases in gastrointestinal transit time and retention and intrascapular brown adipose tissue thermogenesis. Because the mixed-acting sympathomimetics are known to increase blood pressure, these studies examined the ability of L-TYR to influence the pressor responses to PPA, EPH, and AMPH (0.03-1 mg/kg) in urethane-anesthetized rats. Each of the mixed-acting sympathomimetics significantly increased mean arterial, systolic, and diastolic blood pressures when administered alone, but no potentiation by L-TYR was observed. These results demonstrate the inability of L-TYR to potentiate the peripheral vasopressor effects of PPA, EPH, and AMPH. These data, in conjunction with our previous findings, suggest that the potentiation by L-TYR of the mixed-acting sympathomimetics is largely restricted to centrally mediated responses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amphetamine / pharmacology
  • Animals
  • Blood Pressure / drug effects*
  • Dose-Response Relationship, Drug
  • Ephedrine / pharmacology
  • Male
  • Phenylpropanolamine / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Sympathomimetics / pharmacology*
  • Tyrosine / pharmacology*


  • Sympathomimetics
  • Phenylpropanolamine
  • Tyrosine
  • Amphetamine
  • Ephedrine