抄録
The neurochemical changes caused by supplementation of a limiting amino acid (methionine, lysine or tryptophan) to a 5% protein diet (soy protein isolate, corn gluten or gelatin) were investigated. The final levels of each supplemented amino acid were 2- or 4-fold each requirement level in the diets. The supplementation of methionine to the soy protein isolate diet reduced the contents of brain 5-hydroxyindoles (serotonin and 5-hydroxyindole acetic acid (5HIAA)). With lysine supplementation to the corn gluten diet, the brain 5-hydroxyindole contents did not change. Tryptophan supplementation to the gelatin diet caused a significant increase in the brain 5-hydroxyindoles. When rats were fed the soy protein isolate diet supplemented with methionine for a 5-hr period on one day (acute) or on 30 days (chronic), the concentrations of brain 5-hydroxyindoles sharply decreased and remained decreased for 30 days. Good correlations between serum tryptophan, and brain tryptophan and 5-hydroxyindoles were found on multiple regression analysis. These observations indicate that the supplementation of a limiting amino acid to a low protein diet (for improvement of the nutritional quality of the diet) -if the level of each supplemented amino acid is 2- to 4-fold the respective requirement- can cause major neurochemical changes, therefore, these neurochemical parameters may be considered as possible measures for the nutritional and safety evalution of diets.
