Effect of Tyrosine and Threonine on Free Amino Acids in Plasma, Liver, Muscle, and Eye in the Rat

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Abstract
Young rats fed a diet containing 3% tyrosine for 3 to 4 weeks had altered patterns of plasma amino acid concentrations. The greatest change occurred in the concentration of tyrosine, which increased 25- to 80-fold. When 2.5% DL- or 1.25% L-threonine was included in the 3% tyrosine diet, the plasma concentration of tyrosine was much lower than that of rats fed the 3% tyrosine diet without additional threonine; however, the threonine concentration in plasma increased 50- to 100-fold. The tyrosine concentration was increased in liver, muscle, and eye tissue as a result of feeding 3% tyrosine; and threonine supplementation also lowered the tyrosine concentration in these tissues.