Effect of repetitive stunning on myocardial metabolism in pig hearts

Recent animal and clinical studies have suggested that chronic hibernation, a condition of depressed mechanical function and enhanced glycolysis in viable but downregulated myocardium, may result from chronic repetitive ischemia and reperfusion. The present study was conducted to test whether similar trends could be reproduced in an acute animal preparation of repetitive stunning. Eight intact pig hearts were extracorporeally perfused for 115 min and subjected to four cycles of ischemia [60% decrease in anterior descending flow for 5 min each, interspersed with 15 min of aerobic reperfusion]. Each bout of ischemia caused a progressive decline in regional systolic shortening such that systolic shortening was 37% lower at end-reperfusion (P < 0.05 vs. initial conditions). Regional myocardial O2 consumption was reduced during ischemia but was not significantly lower at end-reperfusion compared with that under initial conditions. Fatty acid oxidation was unchanged at any point during the trials. Although glucose utilization was increased by an average of 264% during the four ischemic periods, it was not significantly or progressively increased during the reperfusion periods. Therefore, although this acute stunning protocol depressed mechanical function, it did not cumulatively increase glycolysis during reperfusion. This absence of accelerated glycolysis is at variance with the metabolic findings reported in clinical hibernation and raises concerns regarding this protocol in animal studies designed to simulate short-term hibernation.