The Anabolic Effects of IGF‐1 in Skeletal Muscle After Burn Injury Are not Caused by Increased Cell Volume

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Abstract
Background: In a recent report, insulin‐like growth factor 1 (IGF‐1) stimulated protein synthesis and inhibited protein breakdown in skeletal muscle after burn injury. The mechanism of the anabolic effects of IGF‐1 in skeletal muscle is not known. We tested the hypotheses that IGF‐1 stimulates protein synthesis and inhibits protein breakdown in skeletal muscle secondary to cell swelling and that cell swelling in itself induces an anabolic response in muscle tissue. Methods: Extensor digitorum longus muscles from control and burned rats were incubated in the absence or presence of 1 μg/mL of IGF‐1. Protein synthesis and breakdown rates were determined by measuring incorporation of 14C‐phenylalanine into protein and net release of tyrosine, respectively. Cell volume was measured by determining wet and dry weight and by using 3H‐mannitol as an extracellular marker. Results: IGF‐1 stimulated protein synthesis and inhibited protein breakdown in muscles from nonburned and burned rats without influencing cell volume. Incubating muscles in hypo‐osmotic medium increased cell volume by 17% and inhibited protein breakdown by 14% but did not influence protein synthesis. Conclusions: The anabolic effects of IGF‐1 in skeletal muscle are not caused by increased cell volume. The results differ from those reported previously in liver cells in which the anabolic effects of IGF‐1 were associated with cell swelling. The role of changes in cell volume in the regulation of protein metabolism may be different in skeletal muscle than in other tissues. (Journal of Parenteral and Enteral Nutrition 22:115–119, 1998)