Energy metabolism in reperfused heart muscle: metabolic correlates to return of function

An important question in energy metabolism of the reperfused, previously ischemic myocardium is whether the return of a normal tissue adenosine triphosphate (ATP) content is a prerequisite for normal rates of oxygen consumption (that is, ATP turnover) and cardiac function. To study this problem, isolated working rat hearts were perfused with bicarbonate saline solution containing glucose (10 mM) at near physiologic work load. After 20 minutes, hearts were made totally ischemic by clamping the aortic and atrial lines for 5, 10 or 20 minutes and then were reperfused for another 10 minutes. Heart rate, aortic pressure, cardiac output and myocardial oxygen consumption were measured continuously. Adenine nucleotides, phosphocreatine, glycogen and the products of glycolysis were determined in freeze-clamped tissue extracts. Functional recovery was assessed by return of aortic pressure and oxygen consumption to preischemic values. Time required for return of function after reperfusion was 90 seconds after 5 minutes and 124 seconds after 10 minutes of ischemia. No recovery was observed after 20 minutes of ischemia. Tissue ATP content decreased significantly at the end of 5 (-38%) and 10 (-56%) minutes of ischemia and did not increase significantly at return of aortic pressure and oxygen consumption to preischemic values. Glycogen stores decreased by more than 50% at the end of 10 minutes of ischemia and did not normalize on recovery. In contrast to ATP or glycogen, the phosphocreatine content decreased to even lower levels at the end of ischemia, but returned to levels higher than the control level after recovery from 5 to 10 minutes of ischemia in association with return of function.(ABSTRACT TRUNCATED AT 250 WORDS)