Glucose Metabolism in the Region Recovering from Burn Injury: Effect of Insulin on 2-Deoxyglucose Uptakein Vivo*

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Abstract
The contribution of the burned region to metabolic and endocrine changes after burn injury was investigated in rats and a single hindlimb scald. Three days after the scald, the rats were injected i.v. with a trace amount of 2-deoxy-D-[1-14C]glucose (2-DG) with or without 0.1 U insulin/rat. The animals were killed 25 min after the injection, and cellular uptake of 2-DG/mg dry tissue wt was determined in skeletal muscles and skin of the hindlimbs. Two kinds of muscles were studied: plantaris muscle, which consists predominantly of fast oxidative glycolytic and fast glycolytic fibers; and soleus muscle, which consists primarily of slow oxidative fibers. Under basal conditions, plantaris muscles of the burned limb took up almost 4 times more 2-DG than plantaris muscles of the contralateral unburned limb. Insulin-induced hyperinsulinemia stimulated uptake in muscles of both hindlimbs, but the increment in the plantaris of the burned limb was smaller than that of the unburned limb. Soleus muscles of the burned limb took up 52% more 2-DG than corresponding muscles of the contralateral unburned limb under basal conditions. The administration of insulin led to a 6-fold elevation in 2-DG accumulation by soleus muscles of the unburned limb of burned rats, but the stimulatory effect of insulin was completely absent in the soleus of the burned limb. Since the distal third of the burned limb soleus muscle exhibits degenerative and inflammatory changes, with infiltration by macrophages and fibroblasts, the soleus muscles were divided transversely into thirds, and 2-DG uptake was determined in both the distal third, which is morphologically altered, and the proximal and middle thirds, which are indistinguishable from normal tissue by EM. The middle and distal thirds, but not the proximal third, of the burned limb soleus accumulated more 2-DG under basal conditions than corresponding sections of soleus muscle of the contralateral unburned limb. Exogenous insulin increased uptakes in all thirds of the unburned limb soleus. In contrast, there were no increments in the uptakes in response to insulin in any of the sections of soleus muscle from the burned limb. The basal uptakes by skin of the burned and unburned hindlimbs of burned rats did not differ. Exogenous insulin produced a 49% increase in glucose uptake by skin of the unburned hindlimb, but failed to stimulate the uptake by the skin of the burned limb. Thermal injury restricted to a single hindlimb resulted in 2 alterations in the region of the burn. Basal glucose uptake by skeletal muscles but not the skin of the burned region was elevated. The elevation in glucose uptake seemed to be most pronounced in the portion of the muscle that shows morphological changes and infiltration by nonmuscle cells. All tissues of the burned region showed either reduced responsiveness or complete unresponsiveness to insulin. In muscle, the unresponsiveness to the hormone was not limited to the morphologically altered section and was equally pronounced in sections that were not visibly damaged.