N-acetyl-L-tyrosine as a tyrosine source during total parenteral nutrition in adult rats.

The tyrosine content of parenteral solutions is limited by poor tyrosine solubility. N-acetyl-L-tyrosine has excellent solubility and is a potential source of intravenous tyrosine. Infusion of N-acetyl-U-14C-L-tyrosine as part of a total parenteral nutrition regimen in the rat at a level of 0.5 mmol/kg/day resulted in rapid labeling of tissue tyrosine pools, production of 14CO2, incorporation of 14C-labeled tyrosine into protein, and modest urinary losses (8.3%). Plasma tyrosine levels, however, remained at fasting values (73.8 +/- 5.40 microM). Infusion of N-acetyl-L-tyrosine at 2 mmol/kg/day increased plasma tyrosine above fasting levels (141 +/- 16.1 microM), resulted in a rapid labeling of tissue tyrosine pools, production of 14CO2, and incorporation of 14C-labeled tyrosine into protein. However, urinary losses were higher (16.8%). Rapid utilization of N-acetyl-L-tyrosine was noted at both infusion levels. 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 hydrolysis.