TREATMENT OF BURNED RATS WITH INSULIN-LIKE-GROWTH-FACTOR-I INHIBITS THE CATABOLIC RESPONSE IN SKELETAL-MUSCLE

Thermal injury is associated with a pronounced catabolic response in s keletal muscle, reflecting inhibited protein synthesis and increased p rotein breakdown, in particular myofibrillar protein breakdown. Admini stration of insulin-like growth factor I (IGF-I) has a nitrogen-sparin g effect after burn injury, but the influence of this treatment on pro tein turnover rates in skeletal muscle is not known. In the present st udy, we examined the effect of IGF-I on muscle protein synthesis and b reakdown rates following burn injury in rats. After a 30% total body s urface area burn injury or sham procedure, rats were treated with a co ntinuous infusion of IGF-I (3.5 or 7 mg.kg(-1).24 h(-1)) for 24 h. Pro tein synthesis and breakdown rates were determined in incubated extens or digitorum longus muscles. Burn injury resulted in increased total a nd myofibrillar protein breakdown rates and reduced protein synthesis in muscle. The increase in protein breakdown rates was blocked by both doses of IGF-I and the burn-induced inhibition of muscle protein synt hesis was partially reversed by the higher dose of the hormone. IGF-I did not influence muscle protein turnover rates in nonburned rats. The results suggest that the catabolic response to burn injury in skeleta l muscle can be inhibited by IGF-I.