Effects of Phenylalanine on the Release of Endogenous Dopamine from Rat Striatal Slices

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Abstract
We examined the effect of phenylalanine (50–400 μM) on the electrically stimulated release of endogenous 3,4‐dihydroxyphenylethylamine (dopamine or DA) from superfused rat striatal slices. In the absence of tyrosine, phenylalanine (25 μM) partially sustained DA release, but less well than an equimolar concentration of tyrosine. In the presence of tyrosine (50 μM), phenylalanine (in concentrations of ≥200 μM) inhibited DA release into the superfusate. This inhibition was not associated with changes in tissue levels of tyrosine or DA, nor was it mimicked by addition of high concentrations of tyrosine or leucine to the medium. We conclude that phenylalanine is a less effective precursor of DA in rat striatum than tyrosine and that it can also act to inhibit DA synthesis, depending on its concentration.