1H NMR Measurement of Triacylglycerol Accumulation in the Post-ischemic Canine Heart after Transient Increase of Plasma Lipids

This study tests the hypothesis that increased levels of plasma lipids can accelerate accumulation of myocardial triacylglycerols in post-ischemic but viable myocardium. Two groups of dogs underwent 90 min of left anterior descending coronary artery (LAD) occlusion followed by 240 min of reperfusion. The first group of saline-treated dogs (n=7) had physiological levels of plasma lipids during reperfusion; a second group treated with Liposyn and heparin (n=5) experienced increased plasma lipids during reperfusion. The tansmural content of triacylglycerols was determined during ischemia and reperfusion using1H NMR one-dimensional chemical shift imaging (1D CSI), and at the end of reperfusion using Oil Red-O staining and chemical assay. TTC staining was used to identify the extent of irreversibly injured myocardium. Subepicardial and plasma triacylglycerol content, measured both by 1D CSI and chemically, did not change during reperfusion in saline-treated dogs. Infusing dogs with Liposyn and heparin for 90 min during reperfusion transiently elevated their plasma triacylglycerols, which returned to normal levels following Liposyn wash-out. During Liposyn wash-out, myocardial triacylglycerols measured by 1D CSI preferentially increased in the subepicardium of area-at-risk myocardium (P<0.05). Triacylglycerol content, measured chemically, also increased in area-at-risk compared to non-ischemic subepicardium (P<0.001). Significant endocardial damage occurred in both groups, but elevated levels of plasma lipids did not increase the size of the area-at-risk. Therefore, elevated plasma lipids caused a preferential accumulation of triacylglycerols in area-at-risk myocardium during reperfusion without exacerbating irreversible ischemic injury. These results are consistent with either inhibited fatty acid oxidation or mis-matched fatty acid extraction and oxidation in area-at-risk myocardium.