Abstract
OBJECTIVES: Recent studies suggest that activation of glycogen synthase kinase (GSK)-3β may be involved in burn injury-induced metabolic derangements and protein breakdown in skeletal muscle. However, the mechanism for GSK-3β activation after burn injury is unknown. To investigate the role of inducible nitric oxide synthase (iNOS) in this scenario, a major mediator of inflammation, we examined the effects of a specific inhibitor for iNOS, L-NIL, on GSK-3β activity in skeletal muscle of burned rats. MATERIALS/METHODS: Full-thickness third degree burn injury comprising 40% of total body surface area was produced under anesthesia in male Sprague-Dawley rats (160-190g) by immersing the back of the trunk for 15s and the abdomen for 8s in 80°C water. Burned and sham-burned rats were treated with L-NIL (60mg/kg BW, b.i.d., IP) or phosphate-buffered saline for three days. GSK-3β activity in skeletal muscle was evaluated by immune complex kinase assay, and by phosphorylation status of GSK-3β and its endogenous substrate, glycogen synthase. RESULTS: GSK-3β activity was increased in a time-dependent manner in skeletal muscle after burn injury, concomitant with the induction of iNOS expression. iNOS inhibitor, L-NIL, reverted the elevated GSK-3β activity in skeletal muscle of burned rats, although L-NIL did not alter GSK-3β activity in sham-burned rats. CONCLUSIONS: Our results clearly indicate that iNOS plays an important role in burn injury-induced GSK-3β activation in skeletal muscle. These findings suggest that iNOS may contribute to burn injury-induced metabolic derangements, in part, by activating GSK-3β.