Decrease in plasma phenylalanine and tyrosine after phenylalanine-tyrosine free amino acid solutions in man

After an overnight fast, 5 male healthy subjects ingested increasing amounts of a solution containing a fixed proportion of seven essential amino acids (L-isoleucine, 13.3%; L-leucine, 21.0%; L-lysine, 15.2%; L-methionine, 21.0%; L-threonine, 9.5%; L-tryptophan, 4.8% and L-valine, 15.2%) and lacking phenylalanine and tyrosine. The solutions caused a rapid fall in plasma phenylalanine and tyrosine which was proportional to the total amount of amino acids ingested. Following the highest dose administered (31.5 g) plasma phenylalanine and tyrosine fell to a minimum of, respectively, 12.7% and 29.8% the initial levels and remained markedly reduced at 6 hours after treatment. The decrease of tyrosine and phenylalanine levels was associated with a decrease of systolic and diastolic arterial pressure.