Response to trauma of protein, amino acid, and carbohydrate metabolism in injured and uninjured rat skeletal muscles

Soft tissue injury to one hindlimb produced trauma in rats without affecting their food intake or weight gain. Histologic examination showed damage to the soleus and gastrocnemius muscles but not to the extensor digitorum longus muscle. The protein content of the injured soleus muscle was lower than that of the contralateral soleus at one day after injury, and was reflected in vitro by a faster rate of protein degradation. The injured soleus also showed greater rates of protein synthesis, glucose uptake, glycolysis, oxidation of glucose, pyruvate, and leucine, and de novo synthesis of alanine. During three days after the injury, urinary nitrogen excretion increased progressively and was paralleled by a faster rate of protein degradation in uninjured muscles incubated with glucose, insulin, and amino acids. In these muscles, the inhibition of protein degradation by insulin diminished, while its stimulation of protein synthesis was unaffected. This insensitivity of proteolysis to insulin in trauma can explain the increased rate of this process. The oxidation of glucose and pyruvate were lower in the diaphragms of traumatized than of normal rats incubated with leucine, while glycolysis and uptake of 2-deoxyglucose did not differ. The degradation of leucine and isoleucine was greater in the diaphragms of traumatized animals and was associated with a faster de novo synthesis of alanine. For the uninjured soleus muscles of the traumatized rats, the slower rates of oxidation of glucose, glycolysis, and uptake of 2-deoxyglucose in the presence of insulin showed an insensitivity of glucose metabolism to this hormone. In contrast, no differences were seen in these various metabolic processes between the extensor digitorum longus muscles of traumatized and normal rats. These data suggest that the response of skeletal muscles to trauma may depend on their physiologic and biochemical characteristics.