Comparison of Intravenous Nutrients on Gut Mucosal Protein Synthesis

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Abstract
Background: Total parenteral nutrition (TPN) is associated with atrophy of the intestinal mucosa. This study compared the relative effectiveness of a short‐chain fatty acid (butyrate), a physical mixture of medium‐chain and long‐chain triglycerides, structured lipid, and glutamine as components of a TPN regimen, and their ability to support mucosal protein synthesis. Methods: Rats were parenterally fed one of six isocaloric (1003 kJ/kg·d−1) and isonitrogenous (1.5 g·kg−1·d−1 of nitrogen) diets for 5 days. Diet 1, glucose 90% and long‐chain triglycerides 10% (standard TPN); diet 2, glucose 50% and long‐chain triglycerides 50%; diet 3, glucose 50% and a 50/50 physical mixture of long‐chain and medium‐chain triglycerides 50%; diet 4, glucose 50% and structured lipid 50%; diet 5, glucose 91% and sodium butyrate 9%; and diet 6, same as group 1 except that some of the amino acids were replaced with glycyl glutamine. A control group of rats also underwent catheter placement and were instead fed diet 1 orally for 5 days. Five days after catheterization, all rats were given a 4‐hour constant infusion of [U‐14C]leucine to determine the mucosal fractional protein synthesis rates. Results: (1) Mucosal fractional protein synthesis rates were much higher with the oral diet (control) than with any of the intravenous diets. (2) Diet‐related differences in the mucosal fractional synthesis rates were found with the jejunum and the proximal and distal colon but not with the ileum. (3) Standard TPN was the least effective diet in supporting mucosal protein synthesis. (4) Structured lipid and butyrate were most effective for the jejunum. (5) For the colon, medium‐chain triglycerides and structured lipid were most effective. Conclusion: Standard TPN leads to a decrease in gut mucosal protein synthesis in rats, and this decrease can be partially attenuated by adding nutrients for the gut to the TPN mixture. (Journal of Parenteral and Enteral Nutrition 18:447–452, 1994)