Modulation of skeletal muscle protein synthesis by amino acids and insulin during sepsis

Abstract

Effects of different concentrations of insulin and amino acids on protein synthesis in skeletal muscle of young, fed septic rats were determined in the perfused rat hindlimb. Rates of protein synthesis in gastrocnemius were measured by incorporation of [ 3H-phenylalanine into protein. Perfusion of hindlimb muscles from young, fed control rats with medium containing either insulin and a complete mixture of amino acids at plasma concentration (1x) or a mixture of amino acids at 10-fold (10x) plasma concentration resulted in an approximately twofold stimulation of the rate of protein synthesis. The effect of amino acids on protein synthesis was partly accounted for by elevated concentrations of branched-chain amino acids ([BCAA] leucine, isoleucine, and valine). In young, fed septic rats, the rate of protein synthesis in muscle perfused with buffer containing the normal concentration of amino acids was reduced 40% as compared with control levels ( P < .05). In contrast to controls, addition of insulin (1,000 μU/mL) did not augment protein synthesis in muscle from young, fed septic rats perfused with the complete mixture of amino acids. Addition of insulin 10,000 μU/mL stimulated protein synthesis approximately 80% in gastrocnemius of septic rats ( P < .05). However, the rate of protein synthesis remained less than that observed in young, fed control rats at similar insulin concentrations. Perfusion with medium containing 10x plasma amino acids stimulated protein synthesis approximately fourfold in young, fed septic rats as compared with control animals. In contrast to controls, BCAA at 10x plasma concentration did not augment protein synthesis in young, fed septic rats. There were no significant differences in rates of protein synthesis between control and nonseptic-abscess rats in any of the conditions examined. The results suggest a relative resistance of protein synthesis to the stimulatory effects of insulin or BCAA in muscle from young, fed septic animals, whereas the response to total amino acid supplementation is unaffected by the septic process.