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1 Research and Development Division, Smith Kline & French Laboratories, Philadelphia, Pennsylvania
Groups of Long-Evans strain female weanling rats were maintained for 15 to 17 days on synthetic amino acid diets in which the relative contents of DL-phenylalanine and DL-tryptophan were varied. In addition, the monoamine oxidase inhibitor, trans - 2 - phenylcyclopropylamine (tranylcypromine), was orally administered (2.5 mg/kg), twice a day, starting with the 8th day, to half the animals in each group.
Rat brain norepinephrine (NE) concentration was not significantly influenced by changes in the phenylalanine and/or tryptophan contents of the basal diet. The brain dopamine (DA) concentration, however, was markedly increased in rats maintained on diets enriched with
phenylalanine, but was not significantly affected by a deficiency of dietary phenylalanine or by variations in the dietary content of tryptophan. The brain level of serotonin (5HT) appeared to vary with the relative content of dietary tryptophan and inversely with the relative content of dietary phenylalanine.
The ability of tranylcypromine to increase the concentration of the brain amines was significantly influenced by the dietary content of the 2 amino acids. In general, significantly greater increases of brain 5HT concentration were achieved on diets enriched with tryptophan. Also, markedly higher concentrations of brain DA resulted from diets enriched with phenylalanine. However, diets enriched with phenylalanine gave increases in brain NE concentration which were not substantially different from increases obtained in rats maintained on the basal diet and administered tranylcypromine.
No significant differences in spontaneous motor activity patterns were observed among the rats maintained on the different diets, with or without the concomitant oral administration of tranylcypromine.
Submitted on December 26, 1961
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