Effect of Insulin on Amino Acid Uptake and Protein Turnover in Skeletal Muscle From Septic Rats

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Abstract
• We investigated the effect of different concentrations of insulin (0, 10, 1×102, 1×103, 1×104, and 1×105mU/L [0, 70, 7×102, 7×103, 7×104, and 7×105pmol/L]) on amino acid (α-aminoisobutyric acid) uptake and protein synthesis and breakdown in incubated extensor digitorum longus (EDL) and soleus muscles of rats. We studied three groups: (1) untreated, fed rats; (2) sham-operated rats; and (3) septic rats. Sepsis was induced by cecal ligation and puncture. The α-aminoisobutyric acid uptake was increased by insulin in all three groups. Protein synthesis was maximally stimulated by 30% to 40% by 1×102mU/L (7×102pmol/L) of insulin in all three groups. Protein degradation in soleus muscle was not affected by insulin. In EDL muscles from untreated and sham-operated rats, protein breakdown was reduced by 15% to 20% by 1 × 102mU/L (7×102pmol/L) of insulin. In contrast, protein breakdown was not inhibited by insulin in septic EDL muscle until the concentration of the hormone was increased to 1 ×104mU/L (7×104pmol/L), at which concentration the hormonal effect was less than half that in nonseptic muscle. The results suggest a postreceptor insulin resistance of protein breakdown in septic muscle, while the response to the hormone of amino acid transport and protein synthesis was not altered in sepsis. (Arch Surg1987;122:228-233)