The expression of proinflammatory cytokines in the rat muscle flap with ischemia-reperfusion injury.

Ischemic-reperfusion injury mediated by free radicals and neutrophils is the principal pathway for tissue injury and death. Cytokines influence activity of various cell types during the inflammatory process. In this study, expression of selected proinflammatory cytokines was examined in primary and secondary ischemia in the rat gracilis flap model. Sixty Sprague-Dawley rats were used in the study. Primary ischemia of each gracilis flap was induced by clamping its vascular pedicle for 1 hour. The flap was then replaced and allowed to reperfuse. Twenty-four hours later, a secondary ischemia was induced via vascular clamping for 4 hours. All muscle flaps were biopsied at 4 hours and 18 hours after primary ischemia. After secondary ischemia, each flap was biopsied immediately postevent, at 4 hours, and at 18 hours. Expression of tumor necrosis factor (TNF-alpha), interleukin (IL-1beta), and platelet-derived growth factor (PDGF) mRNA was determined by RT-PCR in each case. An equal sample size of gracilis muscle flaps, elevated in an identical fashion but not subjected to vascular clamping, was examined for baseline gene expression. Results showed that TNF-alpha gene expression was significantly up-regulated at 18 hours after secondary ischemia. IL-1 gene expression was up-regulated at 4 hours after primary ischemia, and was greatest at 4 hours after secondary ischemia. PDGF expression was up-regulated immediately after secondary ischemia, then at 4 hours after secondary ischemia (P < 0.05), and down-regulated during reperfusion. This study delineated changes in the expression of TNF-alpha, IL-1beta, and PDGF mRNA, in both primary and secondary ischemia and reperfusion episodes at several critical time points.