Influence of High Concentrations of Phenylalanine on the Amino Acids of Cerebrospinal Fluid and Blood.

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Abstract
Summary Six phenylketonuric subjects were maintained on a rigorously controlled synthetic diet low in phenylalanine, to which phenylalanine was later added. The concentrations of amino acids in blood and CSF were compared under conditions of normal and high circulating phenylalanine levels. The concentrations of tyrosine, tryptophan, histidine, methionine, citrulline, glutamine, and the dipeptide, carnosine, in the CSF showed significant increases when the PA levels of phenylketonuric patients were permitted to rise 20-fold from normal levels. Only threonine and arginine decreased significantly. In serum the shift to high phenylalanine concentrations resulted in significant changes in only 3 of 18 amino acids. Threonine, histidine, and alanine were decreased. The discrepancy between these changes in serum amino acids and those reported by other investigators are best explained by differences in dietary control.

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