Although considerable attention has focused on obesity, insulin resistance and abnormal lipid metabolism as coronary risk factors, it remains unclear how these pathogenic factors affect the inflammatory response after myocardial ischemia-reperfusion. This study was conducted to evaluate whether these metabolic disorders exacerbate myocardial ischemia-reperfusion injury, and to determine if ischemia-reperfusion injury could be modified with the thiazolidinedione, pioglitazone. Experiments were performed in KK-A(y) and C57BL/6J mice subjected to 40 min of ischemia followed by reperfusion. Infiltration of inflammatory cells in ischemic myocardium, and infarct size 3 days after reperfusion were significantly higher in KK-A(y) than C57BL/6J mice (p<0.05 and p<0.001, respectively). Furthermore, expression of chemokines, inflammatory cytokines and extracellular matrix proteins in ischemic myocardium was significantly higher in KK-A(y) than C57BL/6J mice 1 day after reperfusion. Pioglitazone treatment of KK-A(y) mice for 14 days significantly reduced the accumulation of inflammatory cells in ischemic myocardium, and infarct size 3 days after reperfusion compared to vehicle treatment (p<0.05 and p<0.05, respectively). Pioglitazone also attenuated expression of chemokines, inflammatory cytokines and extracellular matrix proteins in ischemic myocardium 1 day after reperfusion. In vitro experiments demonstrated that tumor necrosis factor-alpha (TNF-alpha) was significantly higher in cultured peritoneal macrophages from KK-A(y) than C57BL/6J mice, and pioglitazone significantly reduced TNF-alpha in macrophages from both types of mice. These findings suggest that metabolic disorders exacerbate ischemia-reperfusion injury as a result of overexpression of inflammatory mediators, and this effect might be improved, in part by the anti-inflammatory effects of pioglitazone.