In this study, we examined the effect of orally administrated dipeptides containing Tyr (Y) on the metabolism of catecholamines in mouse brains. We found that among eight synthetic dipeptides whose sequences are present frequently in soy proteins, Ser-Tyr (SY), Ile-Tyr, and Tyr-Pro had the highest apparent permeability coefficients in monolayers of human intestinal epithelial Caco-2 cells. When administrated orally, SY markedly increased tyrosine content in the cerebral cortex compared to the vehicle control, Ile-Tyr, Tyr-Pro, and Y alone. The oral administration of SY more effectively increased 3-methoxy-4-hydroxyphenylethyleneglycol, the principal metabolite of noradrenaline, in the cerebral cortex and hippocampus than did Ile-Tyr, Tyr-Pro, or Y alone. Central noradrenergic turnover was also markedly stimulated by SY administration. These in vivo observations strongly suggest that SY is more potent in boosting central catecholamine transmission, particularly the noradrenergic system, than Y alone or other dipeptides that include Y.
