Utilization of L-alanyl-L-tyrosine by nephrectomized rats when infused as part of a total parenteral nutrition regimen.

L-Alanyl-L-tyrosine is well utilized as a tyrosine source in parenterally fed rats. Such utilization may depend upon filtration of peptide into the glomerular filtrate, reabsorption into renal epithelial cells, hydrolysis to component amino acids in or at the surface of epithelial cells, and release of component amino acids to the blood. Bilaterially nephrectomized rats were infused with a parenteral solution providing L-alanyl-L-[U-14C]-tyrosine at 0.5 mmoles/kg over a 2 hour period to test this hypothesis. Despite the absence of kidneys, peptide did not accumulate in plasma or tissues. Plasma and liver tyrosine and alanine levels increased significantly over values noted in animals infused without peptide. One-quarter to one-third of the infused radioactivity was released as 14CO2, with the remainder found in the tissues. Between 15 and 51% of radioactivity in individual tissues was free tyrosine, the remainder was incorporated into protein. Isolation of this protein, acid hydrolysis and simultaneous radioactivity-amino acid analysis demonstrated that 94 to 99% of the radioactivity in protein was tyrosine. The data indicate good utilization of alanyl-tyrosine by nephrectomized rats when administered as part of a total parenteral nutrition regimen.