Rat muscle protein turnover and redox state in progressive diabetes

Protein synthesis and degradation, and redox state were measured in soleus and extensor digitorum longus muscles of rats up to 12 days after injection of streptozotocin. Muscle growth was slower in these animals apparently due to slower protein synthesis throughout the duration of diabetes. Up to day 4 after injection of streptozotocin or withdrawal of insulin from treated, diabetic animals, the muscle ratio of lactate/pyruvate, an indicator of the cytoplasmic NAD⁺ redox couple, was lower and protein degradation was faster than in control muscles. Thereafter, the ratio of lactate/pyruvate was greater and protein degradation was slower than in size- or age-matched control muscles. Insulin treatment in vitro or in vivo increased lactate/pyruvate and decreased proteolysis. Therefore, in muscles of streptozotocin-diabetic rats, the initial increase and later fall in proteolysis, and the inhibition of proteolysis by insulin, may correlate with opposite changes in NADH/NAD⁺.