Postoperative parenteral nutrition with high supply of branched-chain amino acids: effects on nitrogen balance and liver protein synthesis.

Branched-chain amino acids (BCAA) stimulate muscle and liver protein synthesis in vitro. The significance of this action in catabolic conditions in vivo remains controversial. The effects of a high supply of BCAA in total parenteral nutrition (TPN) on nitrogen balance and liver protein synthesis were studied in a postoperative rat model. After standard operative trauma TPN was commenced with one of two isocaloric programs (I: 20.1% BCAA and II: 50% BCAA) and continued for 48 hr. The relative rate of liver protein synthesis, measured after TPN in vitro by perfusion with 14C-leucine, was similar in both groups (I: 53.4 +/- 17.3 and II: 49.0 +/- 27.3 arbitrary units of synthesis rate, mean +/- SD). The cumulative nitrogen balance was positive with both regimens and was not improved by the high supply of BCAA (I: 2.02 +/- 0.81 and II: 1.87 +/- 0.63 gN/kg/48 hr mean +/- SD). We conclude that after moderate surgical trauma TPN with a high supply of BCAA offers no advantage over conventional TPN.