Two thirds of patients with acute myocardial infarction or unstable angina pectoris have underlying insulin resistance. Insulin resistance is an independent factor portending poor short and long-term prognosis in these patients. Hearts of insulin-resistant rodents exhibit abnormal carbohydrate and lipid metabolism that may be causally related to impaired functional recovery after ischemia and reperfusion (I/R). However, rodent models are limited by dissimilarities to human cardiac function, metabolism, and gene and protein expression. A large animal model of insulin resistance would be an important tool in bridging rodent and human pathophysiology in this condition. This study will test the hypothesis that diet-induced insulin resistance in pigs causes pathologic alterations of myocardial carbohydrate and lipid metabolism that adversely affect the response to I/R. Pigs fed a diet high in saturated fat and simple sugars develop obesity and insulin resistance over several months;they are compared to lean controls fed a low-fat diet with no added sugar. Under anesthetized conditions, pigs are subjected to myocardial I/R with concomitant measurements of cardiac contractile function, and substrate metabolism. Experiments will determine whether diminished recovery of contractile function in insulin-resistant pigs is related to myocardial insulin resistance due to impaired signaling through the phosphatidylinositol-3-kinase pathway, decreased activity of pyruvate dehydrogenase, altered myocardial free fatty acid metabolism and/or lipid accumulation, or alterations of cardiolipin content and composition. Peroxisome proliferator-activated receptors (PPARs) are critical regulators of substrate metabolism whose expression and function in myocardium may be altered by insulin resistance. Moreover, many patients with insulin resistance are treated with PPAR agonist drugs (fibrates, thiazolidinediones) despite little knowledge of their cardiac effects. Therefore, an additional goal is to determine whether chronic treatment with a PPAR alpha or gamma agonist modifies myocardial metabolic and contractile abnormalities in insulin resistant pigs.
Patients with type 2 diabetes or prediabetes are resistant to the effects of the hormone insulin. Patients with insulin resistance have a poor prognosis after heart attack. Using pigs, this study will determine the ways in which the use of sugars and fats by the heart is altered in insulin resistance, leading to poorer cardiac function after heart attack.
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