A model to study local effects of thermal trauma on muscle metabolism.

To study local effects of burn on muscle in the absence of direct tissue damage, a rat's foot was insulated and one hindlimb was scalded by immersion in 85 degrees C water for 3 sec. Upon recovery, rats exhibited normal locomotion with both hindlimbs in spite of a full-thickness burn from ankle to knee. Thus the effects of the burn were not complicated by disuse atrophy. As in human burns, histological examination of soleus from the burned leg showed it to be morphologically indistinguishable from normal tissue. After 2 or 4 days postburn, the rat was sacrificed and the soleus muscles from the burned and unburned leg were incubated in vitro to measure protein turnover. Muscle from the burned leg demonstrated a maximal increase in protein breakdown 2 days postburn with no change in protein synthesis. At 4 days postburn, protein breakdown remained elevated and synthesis remained unchanged. Since metabolism of contralateral (unburned) muscle was identical to muscle from unburned animals, burn-induced changes must be ascribed to local and not to systemic mediators. Therefore, these experiments demonstrate that local mediators of burn-induced muscle catabolism primarily augment protein breakdown.