Ultrastructure of the rat soleus muscle following a local scald injury

Previous studies demonstrated that 3 days after a 3-second scald of a hindlimb of a rat in 90°C water the soleus muscle of the burned limb, but not of the contralateral unburned limb, showed an elevated rate of in vitro glucose utilization and amino acid release. The aim of the present study was to correlate biochemical findings with the morphology of the muscle.Light and electron microscopic observations indicated that the thermal injury did not alter the structure of the proximal two-thirds of the soleus muscle from the burned limb. The distal part of the muscle exhibited inflammatory and degenerative changes. The extracellular space was dilated and numerous macrophages and fibroblasts were noted in the space. Patent blood vessels were rarely encountered and vessels exhibited varying degrees of endothelial damage. Muscle fibres showed a wide spectrum of morphological alterations. Some fibres appeared normal and others showed disruption of the organization of myofibrils. Some muscle fibres had degenerated, leaving a basement membrane-limited compartment which contained fragments of the muscle fibre and macrophages. Fibrin was noted both in the degenerating muscle fibres and in the extracellular space.It was concluded that soleus muscle from the burned limb is a heterogenous tissue containing both damaged and apparently normal muscle fibres, and non-muscle cells. The presence of macrophages and fibroblasts in the distal portion of soleus muscle could contribute to the increased rate of glucose utilization but further studies will be required to determine whether these cells are fully or only partially responsible for the metabolic alterations observed.