Effects of branched chain amino acid-enriched total parenteral nutrition on amino acid utilization in rats bearing Yoshida sarcoma

We have studied the ability of branched chain amino-acid enriched total parenteral nutrition solutions to improve nutritional status without stimulating tumor growth. Protein kinetics, nitrogen balance, tumor kinetics, fractional synthetic rates of individual tissues, and albumin synthesis were compared in male Sprague-Dawley rats (125-145 g) that had either s.c. Yoshida sarcoma (n = 15) or sham implantations (n = 18). Ten days postinjection, rats were randomly assigned to 2 diet groups and given parenteral infusions of 4 days at 170 kcal/kg.body wt.day as dextrose and 2 g N/kg.body wt.day as either 19 or 50% branched chain amino acid-enriched diet. During the last 4 h of feeding, protein kinetic values were studied using a constant infusion of [14C]tyrosine. Plasma tyrosine appearance, synthesis, and breakdown were unchanged by branched chain amino acid infusion. Percentage of tyrosine flux oxidized and tyrosine oxidation decreased (P less than 0.05) and net tyrosine balance improved (P less than 0.05) in rats receiving the branched chain amino acid-enriched diet. Greater nitrogen balance and lower tumor growth rates were also found in branched chain amino acid-infused rats although not statistically significant. Tumor intracellular specific activity was significantly higher in tumor animals receiving crystalline infusions, suggesting greater tumor protein breakdown with branched chain amino acid-enriched infusion. Fractional synthetic rates of liver, muscle, and tumor were unchanged. Hence, branched chain amino acid-enriched total parenteral nutrition increases amino acid utilization for net protein synthesis principally by reducing oxidation without stimulating tumor growth.