Muscle protein synthesis rate decreases 24 hours after abdominal surgery irrespective of total parenteral nutrition

Background: Muscle protein synthesis rate is known to decrease postoperatively as apart of the catabolic response to trauma Conventional total parenteral nutrition (TPN) in the postoperative period does not seem to counteract the decrease in protein synthesis. However, it is still unclear if ongoing TPN given continuously after surgery would inhibit this fall in muscle protein synthesis. Methods: The rate of protein synthesis in skeletal muscle was determined before and 28 hours after open cholecystectomy, used as a standardized human model of trauma Patients (n = 14) were randomized to receive either TPN continuously throughout the postoperative period or saline as postoperative fluid therapy. The protein synthesis rate was calculated from the increase in enrichment of labeled phenylalanine in protein after an IV flooding dose of [H-2(5)] phenylalanine, 45 mg/kg body weight. Results: The fractional synthesis rate decreased by 31% from 1.74 +/- 0.13% to 1.15 +/- 0.10% per 24 hours in the saline group (p <.02) and by 23% from 1.59 +/- 0.10% to 1.22 +/- 0.07% per 24 hours in the group receiving TPN (p <.01), showing no significant difference between the two groups. Conclusion: A continuous and ongoing infusion of conventional TPN started immediately after surgery did not counteract the obligatory decline of muscle protein synthesis, observed 24 hours postoperatively.