Hyperphenylalaninemia: the effect on cerebral amino acid levels during development

The subcutaneous administration of phenylalanine to adult or 20-day-old rats produces a 20- to 25-fold rise in cerebral phenylalanine with only a two- to five-fold rise in tyrosine.The branched-chain amino acids decrease in the brains of these animals but levels of nonessential amino acids are unchanged.In 10-day-old rats subcutaneous phenylalanine administration produces a greater increase in cerebral phenylalanine and tyrosine and has less effect on the branched-chain amino acids, but causes marked decreases in nonessential amino acids. The findings suggest that the permanent defect in myelin formation produced by hyperphenylalaninemia in the newborn rat may be related to altered intermediary metabolism resulting from the fall in nonessential amino acids.