TRICARBOXYLIC-ACID CYCLE ACTIVITY IN POSTISCHEMIC RAT HEARTS

Background. Although myocardial oxidative tricarboxylic acid (TCA) cycle activity and contractile function are closely linked in normal cardiac muscle, their relation during postischemic reperfusion, when contractility often is reduced, is not well defined. Methods and Results. To test the hypothesis that oxidative TCA cycle flux is reduced in reperfused myocardium with persistent contractile dysfunction, TCA cycle flux was measured by analyzing the time course of sequential myocardial glutamate labeling during C-13-labeled substrate infusion with C-13 nuclear magnetic resonance spectroscopy in beating isolated rat hearts at 37-degrees-C. Total TCA cycle flux, indexed by both empirical and mathematical modeling analyses of the C-13 data, was not reduced but rather increased in hearts reperfused after 17-20 minutes of ischemia (left ventricular pressure, 73+/-5% of preischemic values) compared with flux in developed pressure-matched controls (e.g., total flux, 2.5+/-0.4 versus 1.6+/-0.1 mumol . min-1 . g wet wt-1, respectively; P<0.01). No TCA cycle activity was detectable by C-13 nuclear magnetic resonance in hearts reperfused after 40-45 minutes of ischemia, which lacked contractile recovery and had ultrastructural evidence of irreversible injury. Conclusions. These results suggest that TCA cycle activity is not persistently decreased in dysfunctional reperfused myocardium after a brief ischemic episode and therefore cannot account for the reduced contractile function at that time.