Relative influence of glucose and insulin on peripheral amino acid metabolism in severely burned patients

BACKGROUND: Protein catabolism and glucose intolerance are prominent in critically injured patients. The objective of this study was to assess if glucose or insulin availability influences the extent of protein catabolism in hypermetabolic patients. METHODS: Amino acid net balance from the leg was quantitated in 6 severe burn victims. Furthermore, whole body and leg protein kinetics were assessed with 2H5 phenylalanine and 15N alanine. Measurements were obtained after a 9-hour fast, during an IV glucose infusion (30 micromol/kg per minute), and during a hyperinsulinemic (500 mIU/kg per minute) euglycemic clamp. RESULTS: Compared with fasting values, the administration of glucose resulted in a significantly increased efflux of amino acids from the leg. In contrast, insulin administration significantly decreased the cumulative net efflux of amino acids. During hyperinsulinemia, isotopic measurements demonstrated a significant decrease in alanine appearance and an increase in phenylalanine disappearance into the leg. CONCLUSIONS: These findings demonstrate that in critically injured patients, acute hyperglycemia increases muscle catabolism despite an endogenous insulin response. In contrast, exogenous insulin given in sufficient amount impedes muscle protein loss. The mechanism for this anabolic effect of insulin may vary between different amino acids. The efflux of amino acids from the leg of severe burn victims is exacerbated by hyperglycemia, whereas hyperinsulinemia and euglycemia attenuated muscle protein loss. These results reveal a possible association between acute hyperglycemia and muscle catabolism in hypermetabolic patients.