title: Parenteral glycyl-L-tyrosine maintains tyrosine pools and supports growth and nitrogen balance in phenylalanine-deficient rats.
abstract: Poor solubility hampers the addition of sufficient amounts of free tyrosine to parenteral amino solutions. We investigated the use of a highly soluble synthetic dipeptide, glycyl-L-tyrosine, as a parenteral tyrosine source in 18 male Wistar rats (body weight 180-200 g). The animals were randomized into three equal groups and catheterized to facilitate isoenergetic (1.2 MJ.kg-1.d-1) and isonitrogenous (1.25 g nitrogen.kg-1.d-1) total parenteral nutrition for 7 d. Controls (Group 1) received a complete amino acid solution, Group 2 received the same solution deficient in phenylalanine (nitrogen replaced with glycine), and group 3 received the phenylalanine-deficient solution supplemented with glycyl-L-tyrosine. Between d 4 and 7, weight gain and nitrogen retention were lower in Group 2 and in Group 1 or 3. In plasma and organ samples obtained at the end of the study, amino acids and dipeptides were analyzed by means of reversed phase-HPLC. In Group 2, phenylalanine and tyrosine concentrations were lower than in controls in plasma, muscle and kidney; in liver, only the tyrosine concentration was lower compared with controls. With glycyl-L-tyrosine supplementation, plasma, liver and kidney tyrosine concentrations and the phenylalanine:tyrosine ratio were normal. Intact glycyl-L-tyrosine was not detectable, suggesting a virtually quantitative elimination or utilization of the infused dipeptide. The results indicate that in phenylalanine-deficient rats, parenteral glycyl-L-tyrosine rapidly provides free tyrosine to facilitate normal growth, promote nitrogen metabolism and maintain intra- and extracellular tyrosine pools.
authors.affiliation: Institute for Biological Chemistry and Nutrition, University of Hohenheim, Stuttgart, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Stehle
authors.forename: S
authors.initials: S
authors.lastname: Weber
authors.forename: P
authors.initials: P
authors.lastname: Fürst
mesh_terms: D000596:Amino Acids / Q000097:blood / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001835:Body Weight / Q000187:drug effects / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D004151:Dipeptides / Q000008:administration & dosage / Q000494:pharmacology*; D006128:Growth / Q000187:drug effects* / Q000502:physiology; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010288:Parenteral Nutrition; D010649:Phenylalanine / Q000097:blood / Q000172:deficiency* / Q000502:physiology; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D014443:Tyrosine / Q000097:blood / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D004151:Dipeptides; D014443:Tyrosine; D010649:Phenylalanine; C022013:glycyltyrosine; D009584:Nitrogen