Altered protein kinetics in vivo after single-limb burn injury.

Recovery from burn injury is associated with stimulated whole-body protein turnover. Since skeletal muscle and liver are the tissues most likely to influence whole-body measurements, we studied protein kinetics in soleus and plantaris muscles as well as liver 3 days after a 3 s burn on one hindlimb of the rat. Muscles from both the burned and unburned limbs of burned rats were compared with those of uninjured controls to distinguish between local and systemic factors involved. The following measurements were performed: (1) fractional growth rate of the tissue protein pool, determined from tissue protein content on days 2, 3 and 4; (2) fractional protein-synthetic rate, measured by [14C]tyrosine constant infusion on day 3; (3) fractional protein-degradation rate, calculated from the difference between the rates of protein synthesis and growth. Protein growth by soleus and plantaris muscles of control rats and unburned limb of burned rats was not paralleled by those in the burned limb, which showed progressive atrophy between 2 and 4 days post-burn (P less than 0.005). Protein synthesis by soleus but not plantaris muscle in the unburned limb of burned rats was enhanced by 62% (P less than 0.04) above control. Protein synthesis by burned-limb soleus and plantaris muscles was elevated by 114% (P less than 0.001) and 67% (P less than 0.02) respectively above control. Protein degradation by both soleus and plantaris muscles in the unburned limb of burned rats did not differ from control. In contrast, that of soleus and plantaris muscles in the burned limb was stimulated by 230% (P less than 0.001) and 164% (P less than 0.001) respectively compared with controls. Protein turnover of soleus muscles in both control and burned rats was more rapid than in corresponding plantaris muscles. Liver protein mass exhibited steady growth in control rats, but remained unchanged in burned animals between 2 and 4 days post-burn. Liver protein synthesis in burned rats was elevated by 56% (P less than 0.01) and protein breakdown was stimulated by 61% (P less than 0.002) above those of controls. The data indicate that both local and systemic factors influence tissue protein turnover in animals recovering from a single-hindlimb scald.