L-alanyl-L-tyrosine as a tyrosine source during total parenteral nutrition. Infusion at 0.5 and 2 mmoles/kg/day in adult rats.

Tyrosine peptides, such as L-alanyl-L-tyrosine, have excellent solubility and are potential sources of iv tyrosine. Infusion of L-alanyl-L-U-14C-tyrosine as part of a total parenteral nutrition regimen in the rat at a level of 0.5 mmole/kg/day resulted in rapid labeling of tissue tyrosine pools, production of 14CO2, incorporation of 14C-labeled tyrosine into protein, and minimal urinary losses (7.7%). Plasma tyrosine levels, however, remained at fasting. Infusion of L-alanyl-L-tyrosine at 2 mmole/kg/day increased plasma tyrosine above fasting levels and maintained tissue tyrosine at levels seen in orally fed control animals without increasing the percent lost in urine (5.5%). Rapid utilization of L-alanyl-L-tyrosine was noted at both infusion levels with no accumulation of peptide noted in plasma. Plasma and tissue free tyrosine pools were rapidly labeled, as was tissue protein. Radioactivity incorporated in tissue protein was shown to be tyrosine after acid hyrolysis.