L-tyrosine fails to potentiate several peripheral actions of the sympathomimetics.
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.
Hull
K M
KM
Department of Pharmacology, Massachusetts College of Pharmacy, Boston 02115.
Maher
T J
TJ
D002001:Adipose Tissue, Brown / Q000187:drug effects; D000818:Animals; D001067:Appetite Depressants / Q000494:pharmacology*; D001833:Body Temperature Regulation / Q000187:drug effects; D003913:Dextroamphetamine / Q000494:pharmacology; D004357:Drug Synergism; D004809:Ephedrine / Q000494:pharmacology; D005772:Gastrointestinal Transit / Q000187:drug effects; D008297:Male; D010525:Peripheral Nerves / Q000187:drug effects*; D010665:Phenylpropanolamine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013270:Stomach / Q000187:drug effects; D013566:Sympathomimetics / Q000494:pharmacology*; D014443:Tyrosine / Q000494:pharmacology*; D014633:Valine / Q000494:pharmacology
D001067:Appetite Depressants; D013566:Sympathomimetics; D010665:Phenylpropanolamine; D014443:Tyrosine; D004809:Ephedrine; D014633:Valine; D003913:Dextroamphetamine