Role of glucose metabolism in the recovery of postischemic LV mechanical function: effects of insulin and other metabolic modulators.

The role of proton (H+) production from glucose metabolism in the recovery of myocardial function during postischemic reperfusion and its alteration by insulin and other metabolic modulators were examined. Rat hearts were perfused in vitro with Krebs-Henseleit solution containing palmitate (1.2 mmol/l) and glucose (11 mmol/l) under nonischemic conditions or during reperfusion following no-flow ischemia. Perfusate contained normal insulin (n-Ins, 50 mU/l), zero insulin (0-Ins), or supplemental insulin (s-Ins, 1,000 mU/l) or other metabolic modulators [dichloroacetate (DCA) at 3 mmol/l, oxfenicine at 1 mmol/l, and N6-cyclohexyladenosine (CHA) at 0.5 micromol/l]. Relative to n-Ins, 0-Ins depressed rates of glycolysis and glucose oxidation in nonischemic hearts and impaired recovery of postischemic function. Relative to n-Ins, s-Ins did not affect aerobic glucose metabolism and did not improve recovery when present during reperfusion. When present during ischemia and reperfusion, s-Ins impaired recovery. Combinations of metabolic modulators with s-Ins stimulated glucose oxidation approximately 2.5-fold in nonischemic hearts and reduced H+ production. DCA and CHA, in combination with s-Ins, improved recovery of function, but addition of oxfenicine to this combination provided no further benefit. Although DCA and CHA were each partially protective in hearts perfused with n-Ins, optimal protection was achieved with DCA + CHA; recovery of function was inversely proportional to H+ production during reperfusion. Although supplemental insulin is not beneficial, elimination of H+ production from glucose metabolism by simultaneous inhibition of glycolysis and stimulation of glucose oxidation optimizes recovery of postischemic mechanical function.