Insulin's anabolic effect is influenced by route of administration of nutrients

OBJECTIVE: To determine if the anabolic effects of intravenous insulin on protein kinetics could be exploited in the enterally fed trauma victim. DESIGN: Randomized, crossover control protocol. SETTING: Level I trauma center. PATIENTS: Ten trauma patients with an Injury Severity Score higher than 20. Exclusion criteria included diabetes mellitus, pregnancy, steroid use, and aged younger than 18 years or older than 65 years. INTERVENTIONS: Within the first 24 hours of admission to the intensive care unit, each patient had a transpyloric feeding tube inserted radiographically. Enteral nutrition was provided with a protein supplement (Ensure, Ross Laboratories, Columbus, Ohio) and Promod, supplemented with protein powder to supply 1.5 g/kg per day of protein and 156.9 kJ/kg per day. Intravenous insulin was provided at 0.043 U/kg per hour beginning on the second or fourth day. MAIN OUTCOME MEASURES: Urinary nitrogen balance and 3-methylhistidine excretion rates were measured at the end of the third and fifth days. Plasma glucose, insulin, and C-peptide levels were obtained at these same times. RESULTS: Urinary nitrogen balance was not significantly different with or without the administration of insulin (-4.58+/-50.1 mg/kg per day vs -9.38+/-50.9 mg/kg per day, respectively). 3-Methylhistidine excretion rates did not change significantly with or without the administration of insulin (5.77+/-0.67 micromol/kg per day vs 6.15+/-0.43 micromol/kg per day, respectively). Serum insulin levels did not differ significantly when exogenous infusions were added (57.8+/-17.9 microU/mL vs 82.1+/-44.9 microU/mL), but serum C-peptide levels did decrease significantly when exogenous insulin was added (5.11+/-3.2 microU/mL vs 10.28+/-3.5 microU/mL; P = .04). Serum glucose levels decreased significantly when insulin was administered (5.8+/-0.4 mmol/L [104.6+/-7.2 mg/dL] vs 7.7+/-0.4 mmol/L [138.1+/-7.4 mg/dL; P =.004). CONCLUSION: The anabolic effect of intravenous insulin on protein kinetics is not evident when nutrition is provided enterally in the trauma victim.