THE ANABOLIC EFFECTS OF IGF-1 IN SKELETAL-MUSCLE AFTER BURN INJURY ARE NOT CAUSED BY INCREASED CELL-VOLUME

Background: In a recent report, insulin-like growth factor 1 (IGF-1) s timulated protein synthesis and inhibited protein breakdown in skeleta l muscle after burn injury. The mechanism of the anabolic effects of I GF-1 in skeletal muscle is not known. We tested the hypotheses that IG F-1 stimulates protein synthesis and inhibits protein breakdown in ske letal muscle secondary to cell swelling and that cell swelling in itse lf induces an anabolic response in muscle tissue. Methods: Extensor di gitorum longus muscles from control and burned rats were incubated in the absence or presence of 1 mu g/mL of IGF-1. Protein synthesis and b reakdown rates were determined by measuring incorporation of C-14-phen ylalanine into protein and net release of tyrosine, respectively. Cell volume was measured by determining wet and dry weight and by using H- 3-mannitol as an extracellular marker. Results: IGF-1 stimulated prote in synthesis and inhibited protein breakdown in muscles from nonburned and burned rats without influencing cell volume. Incubating muscles i n hypo-osmotic medium increased cell volume by 17% and inhibited prote in breakdown by 14% but did not influence protein synthesis. Conclusio ns: The anabolic effects of IGF-1 in skeletal muscle are not caused by increased cell volume. The results differ from those reported previou sly in liver cells in which the anabolic effects of IGF-1 were associa ted with cell swelling. The role of changes in cell volume in the regu lation of protein metabolism may be different in skeletal muscle than in other tissues.