Protein metabolism during total parenteral nutrition (TPN) in injured rats using medium-chain triglycerides

There are metabolic limitations to the infusion of large quantities of dextrose in critically ill patients receiving total parenteral nutrition. Of the alternative, nonprotein lipid sources, medium chain triglycerides (carbon chain length 8 and 10) are more rapidly oxidized and are deposited in the adipose tissue at rates much less than long chain triglycerides. In rats with burn injury receiving hypocaloric (dextrose and amino acids) parenteral feeding, we studied the changes in protein metabolism as a result of increasing the caloric intake by 33% by the addition of either dextrose, a soybean oil emulsion, a medium chain triglyceride emulsion, or a structured lipid emulsion of triglycerides synthesized from safflower oil (40%) and medium chain triglycerides (60%). Changes in body weight, blood glucose concentration, beta-hydroxybutyrate, lactate, amino acids, insulin, albumin, liver protein content, and nitrogen balance were measured during three days of feeding. Whole body leucine kinetics and muscle protein fractional synthetic rate were evaluated using a constant intravenous infusion of L-[1-14C]leucine. The addition of dextrose or soybean oil emulsion produced a significant increase in body weight and liver nitrogen but did not change albumin concentrations or leucine kinetics compared to those of the hypocaloric feeding group. Rats receiving medium chain triglycerides and structured lipid emulsions showed a reduction in branched chain amino acid concentrations and an improvement in serum albumin levels. However, the rats receiving the structured lipid emulsion also showed increased body weight, had a significant decrease in leucine oxidation, and showed a three day cumulative nitrogen balance significantly greater than zero.(ABSTRACT TRUNCATED AT 250 WORDS)