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Use of the Soluble Peptide γ‐L‐Glutamyl‐L‐Tyrosine to Provide Tyrosine in Total Parenteral Nutrition in Rats
Author(s) -
Radmacher Paula G.,
Hilton Mary A.,
Hilton Frederick K.,
Duncan Scott D.,
Adamkin David H.
Publication year - 1993
Publication title -
journal of parenteral and enteral nutrition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.935
H-Index - 98
eISSN - 1941-2444
pISSN - 0148-6071
DOI - 10.1177/0148607193017004337
Subject(s) - tyrosine , parenteral nutrition , phenylalanine , amino acid , chemistry , medicine , endocrinology , peptide , phenylketonurias , saline , tyrosine hydroxylase , biochemistry , enzyme
Limited solubility restricts amounts of tyrosine (Tyr) in amino acid solutions used in total parenteral nutrition (TPN). Excess phenylalanine (Phe) is included in TPN for conversion to Tyr by liver Phe hydroxylase. However, this conversion is limited, especially in infants. We have confirmed that infants receiving TPN have low Tyr concentrations and high Phe/Tyr ratios in plasma compared with published values for enterally fed neonates. Tyr is important in the synthesis of proteins and other biomolecules, including catecholamines in the brain. We tested the soluble peptide γ‐glutamyl‐tyrosine (Glu(Tyr)) as a possible precursor of Tyr in TPN. Groups of five rats were given infusions of TPN containing an amino acid mixture simulating a commercial formulation (group A), TPN in which Glu(Tyr) was substituted for half the Phe in the group A solution) (group B), or saline (group C). Control animals (group C) were fed rodent chow. Blood was sampled at 0 time and daily for 4 days. Brains were collected at 96 hours, and aromatic amino acids in plasma and brains were measured by high‐performance liquid chromatography. Throughout the experiment, plasma of animals in group A had significantly elevated Phe and reduced Tyr concentrations compared with control values; plasma concentrations in groups B and C were similar. In groups A and B, brain Tyr levels were 31% and 63% of control values, respectively. In group B, Glu(Tyr) was not detected in brains. These data suggest that supplementing current TPN mixtures with Glu(Tyr), which is stable in solution, can produce normal plasma Tyr concentrations and Phe/ Tyr ratios and improve the supply of Tyr to the brain. (Journal of Parenteral and Enteral Nutrition 17:337–344, 1993)