Catecholamine synthesis and transmission in the brain are influenced by the availability of Tyr in the body. In this study, we compared the effects of oral administration of Tyr-containing dipeptides Ile-Tyr, Ser-Tyr, and Tyr-Pro with Tyr alone on catecholamine metabolism in the mouse brainstem. Among these dipeptides, Ile-Tyr administration led to increases in dopamine, the dopamine metabolites homovanillic acid, and 3,4-dihydroxyphenylacetic acid, compared to administration of Ser-Tyr, Tyr-Pro, or Tyr alone. In comparison, administration of Ser-Tyr induced significantly increasing noradrenaline turnover, while Tyr-Pro administration suppressed dopamine turnover. Therefore, oral administration of Ile-Tyr, Ser-Tyr, and Tyr-Pro differentially affected metabolism of dopamine and noradrenaline. These observations strongly suggest that Tyr-containing dipeptides exert distinct effects on catecholamine metabolism in the brainstem when ingested orally.
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