Effect of amino acid infusion on human postoperative colon protein synthesis in situ

BACKGROUND: Amino acids are an integral part of parenteral nutrition because of their anabolic action helping to conserve body protein after surgical stress. At the gastrointestinal tract, an adequate supply of amino acids may be particularly important because of the gut's high rate of protein turnover, cell division, and proliferation. However, no information is available about the effects of amino acids on human intestinal protein metabolism after surgery. METHODS: Studies were performed in postabsorptive patients 8-10 days after major abdominal surgery. Mass spectrometry techniques (capillary gas chromatography/combustion isotope ratio mass spectrometry) were used to directly determine the incorporation rate of 1-[13C]-leucine into colon mucosal protein. All subjects had a colostomy, which allowed easy access to the colon mucosa, and consecutive sampling from the same tissue was performed during continuous isotope infusion (0.16 micromol/kg min). Isotopic enrichments were determined at baseline and after a 4-hour infusion of amino acids or after infusion of saline (control group). RESULTS: Compared with baseline, infusion of amino acids reduced fractional colon protein synthesis significantly by -29.2 +/- 8.3%. This decrease was also significantly different from the corresponding (insignificant) change during saline infusion (+19.4 +/- 26.9%, p < .05 vs amino acid group). CONCLUSIONS: After surgery, an amino acid infusion acutely reduces postoperative colon protein synthesis. This effect possibly may be attributed to interactions of specific amino acids (glutamine) with an altered intestinal immune system and enterocyte activity.