METABOLIC-FATE OF GLUCOSE IN REVERSIBLE LOW-FLOW ISCHEMIA OF THE ISOLATED WORKING RAT-HEART

The acute adaptation of myocardial glucose metabolism in response to l ow-flow ischemia and reperfusion was investigated in isolated working rat hearts perfused with bicarbonate saline containing glucose (10 mM) and insulin (40 mu U/ml). Reversible low-flow ischemia was induced by reducing coronary perfusion pressure from 100 to 35 cmH(2)O. Tritiate d glucose was used to assess rates of glucose transport and phosphoryl ation, flux from glucose to pyruvate, and oxidation of exogenous gluco se. Rates of glycogen synthesis and glycolysis were also assessed. Wit h ischemia, cardiac power decreased by more than two-thirds. Rates of glucose uptake and flux from glucose to pyruvate remained unchanged, w hile glucose oxidation declined by 61%. Rates of lactate release more than doubled, and fractional enrichment of glycogen remained the same. During reperfusion, glucose oxidation returned to the preischemic val ues. When isoproterenol was added during ischemia, glucose uptake incr eased, glycogen decreased, and lactate release increased. No effect wa s seen with pacing. We conclude that during low-flow ischemia and with glucose as the only exogenous substrate, net glucose uptake remains u nchanged. There is a reversible redirection between glycolysis and glu cose oxidation, while glycogen synthesis continues during ischemia and is enhanced with reperfusion.