Whole-body nitrogen and tyrosine metabolism in surgical patients receiving branched-chain amino acid solutions
S. P. Desai, B. R. Bistrian, L. L. Moldawer and G. L. Blackburn
Fifteen patients undergoing gastric bypass surgery for morbid obesity
received preoperatively a standard crystalline amino acid solution
containing 15.6% branched-chain amino acids. During the first five
postoperative days, the patients were randomized to receive one of three
amino acid solutions (9.0 to 10.3 g of nitrogen per day) of different
branched-chain amino acid content. The branched-chain amino acid
concentrations of the mixtures were 15.6%, 50%, and 100% by weight with
five patients in each group. Whole-body amino acid appearance and oxidation
were estimated using a continuous intravenous infusion of
L-(U-14C)-tyrosine preoperatively and on the third postoperative day. Daily
postoperative nitrogen balance, fractional albumin renewal rate, and
whole-body tyrosine appearance, oxidation, and incorporation into protein
were not significantly different among the three groups. This study
suggests that an adequate nitrogen intake of a balanced amino acid mixture,
as well as a solution enriched with branched-chain amino acids, maintains
protein homeostasis and supports protein synthesis similarly in
well-nourished patients following major abdominal surgery. A diet
containing only branched-chain amino acids in isomolar ratios was as
effective at maintaining protein retention and whole-body protein synthesis
and albumin renewal postoperatively when compared with a standard amino
acid formula.
