The impact of
renal failure on the elimination and hydrolysis of three sources of
tyrosine for
parenteral nutrition, the
dipeptides alanyltyrosine (
Ala-Tyr),
glycyltyrosine (
Gly-Tyr), and
N-acetyltyrosine (NAc-Tyr) was investigated in eight patients on regular
hemodialysis therapy (HD) and seven healthy controls (CON). In CON, whole body clearance (Ctot) of
Ala-Tyr (3,169 +/- 198 ml/min) was higher than
Gly-Tyr (1,781 +/- 184, P less than 0.001), and both exceeded NAc-Tyr (284 +/- 24, P less than 0.001). In HD, Ctot of
Ala-Tyr was not different from CON, but Ctot of
Gly-Tyr (858 +/- 73, P less than 0.001) and NAc-Tyr (129 +/- 30, P less than 0.02) was decreased. The rise in plasma levels of constituent
amino acids was higher in
Ala-Tyr vs.
Gly-Tyr (P less than 0.01). In HD, the pattern was similar, although the increase in Tyr was less than in CON. Plasma Tyr did not increase with NAc-Tyr in either group. Urinary loss of
peptides was neglible, but 60% of NAc-Tyr infused was excreted by CON. The half-life of
peptides incubated in CON and HD plasma was unchanged for
Ala-Tyr (12.3 +/- 0.9 vs. 14.6 +/- 1.9 min) and prolonged for
Gly-Tyr in HD (101.7 +/- 4.9 vs. 131.3 +/- 12, P less than 0.05). Thus
renal failure does not impair
Ala-Tyr disposal and delays
Gly-Tyr utilization. These differential effects on
peptide assimilation underscore the importance of
peptide structure on metabolism. Both
peptides, but not NAc-Tyr, may serve as a nutritional substrate in
renal failure patients.