THE EFFECTS OF INSULIN ON MYOCARDIAL-METABOLISM AND ACIDOSIS IN NORMOXIA AND ISCHEMIA - A P-31-NMR STUDY

The effect of insulin on the perfused rat heart during normoxia and total ischemia was studied by 31P-NMR. During normoxic perfusion, insulin increased the phosphocreatine to ATP ratio at the expense of Pi, when glucose was the substrate. No change was observed when acetate was used as the sole substrate. The intracellular pH (as measured from the position of the 2-deoxyglucose 6-phosphate resonance peak) was unaffected by insulin treatment. Infusion of insulin prior to ischemia caused an increase in the rate and extent of acidosis during the period of no flow while the rate of ATP depletion was decreased. Freeze-clamped studies showed an increase in glycogen levels upon insulin treatment of the glucose perfused rat heart. During ischemia, a decrease in glycogen content concomitant with an increase in lactate was observed. The accessibility of glycogen to phosphorylase during ischemia is increased as a result of insulin treatment. The control of glycolysis during ischemia is discussed with respect to the content and structure of glycogen in heart tissue.