Effects of Major Skeletal Trauma on Whole Body Protein Turnover in Man Measured by L-[1,14C]-leucine

Skeletal trauma induces excessive urinary nitrogen losses and is thought to stimulate the oxidation of the branched chain amino acids. This study was undertaken to quantitate whole body protein turnover rates and leucine metabolism during the peak nitrogen loss period following skeletal trauma. Quantitation was done in eight healthy and six trauma subjects, who received D5W as their only nutrition for 72 hours, using a 10-hour continuous infusion of L-[1,14C]-Leucine. The controls lost an average of 6 gm of nitrogen/day and the trauma patients 25 gm of nitrogen/day on the study day. Trauma was shown to elevate plasma leucine by 76%, increase the leucine flux through the free leucine pool by 86%, and accelerate leucine oxidation by 277% over the values for controls. Trauma also produced a 50% increase in whole body protein synthesis and a 79% increase in protein breakdown. The data clearly define significant increases in both the protein synthetic and catabolic rates in trauma with a greater increase occurring in catabolism. This is similar to findings for protein turnover in sepsis and burn injury, but is different from that found in elective surgery. A striking aspect of our data is the indication that women do not exhibit the same response to injury that men do. This suggestion, however, is based on a small sample.