The influence of L-tryptophan and monoamine oxidase inhibitors on catecholamine metabolism in rat brain.
1. L-Tryptophan (100 mg/kg) was administered to rats with or without pretreatment with a monoamine oxidase inhibitor and the concentration of 5-hydroxyindoleacetic acid, homovanillic acid, dihydroxyphenylacetic acid, 3-methoxy 4-hydroxyphenyl glycol, normetanephrine, noradrenaline and dopamine measured in whole brain one hour later. 2. L-Tryptophan increased the concentration of 5-hydroxyindoleacetic acid, homovanillic acid, dihydroxyphenylacetic acid, 3-methoxy 4-hydroxyphenyl glycol and normetanephrine. The concentration of noradrenaline did not change whilst that of dopamine increased significantly. 3. In animals pretreated chronically with a monoamine oxidase inhibitor, tryptophan increased the concentration of dihydroxyphenylacetic acid and homovanillic acid compared to monoamine oxidase alone. 4. The results suggest either a release of dopamine and noradrenaline by 5-hydroxytryptamine, with a compensatory increase in their synthesis, or an increase in the firing of dopaminergic and noradrenergic neurones after L-tryptophan.
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D008297:Male; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D010624:Phenelzine / Q000494:pharmacology; D051381:Rats; D014364:Tryptophan / Q000494:pharmacology*
D002395:Catecholamines; D008996:Monoamine Oxidase Inhibitors; D014364:Tryptophan; D010624:Phenelzine