Branched chain amino acid uptake and muscle free amino acid concentrations predict postoperative muscle nitrogen balance.

Amino acid solutions rich in branched chain amino acids (BCAA) are commonly utilized both clinically and in experimental protocols in an attempt to reduce skeletal muscle and whole body protein catabolism. To investigate the effectiveness of BCAA infusion, amino acid formulas containing varying concentrations of BCAA were given during operation in this study to three groups of dogs undergoing a standard laparotomy and retroperitoneal dissection. A fourth group was given saline alone. With the use of previously described hindquarter flux techniques, individual and total amino acid nitrogen exchange rates were measured and utilized in estimating skeletal muscle protein catabolism. Intracellular free amino acid concentrations were measured in percutaneous muscle biopsy samples. Although there was no relationship with the rate of BCAA infusion, there was a significant correlation between the rate of BCAA uptake by muscle and diminished total nitrogen release from hindquarter skeletal muscle after operation. There was also a significant relationship between muscle nitrogen balance and the postoperative change in the muscle concentration of either total amino acids or the single amino acid glutamine. When combined in a single equation, BCAA uptake and the change in muscle free amino acid concentration predict skeletal muscle nitrogen release with an r = 0.86. Thus, the rate of BCAA uptake and the free glutamine or total amino acid concentration in muscle appear to be independent predictors of muscle nitrogen balance. The nitrogen-sparing effect of BCAA in skeletal muscle is unrelated to infusion concentration or rate of infusion.