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.