Enhancement of brain serotonin by long term oral administration of tryptophan produces no effect on food intake

ABSTRACT

L-tryptophan [TRP] is widely used to enhance serotonin mediated brain functions. In the present study effects of oral administration of TRP [100mg/kg] daily for 5 weeks, were investigated on the food intake, growth rate and brain indoleamine metabolism in young rats. TRP ingestion significantly increased growth rate but did not alter food intake in rats. The levels of TRP and 5-hydroxytryptamine [5-HT] were higher in the hypothalamus of TRP treated rats. Increases of 5-hydroxyindole acetic acid [5-HIAA] were not significant. TRP, 5-HT and 5-HIAA all increased in the rest of the brain of TRP treated rats. The present study shows that long term TRP administration though increases brain 5-HT metabolism and turnover but functional responses to 5-HT are not necessarily increased