EFFECT OF REPETITIVE STUNNING ON MYOCARDIAL-METABOLISM IN PIG HEARTS

Recent animal and clinical studies have suggested that chronic hiberna tion, a condition of depressed mechanical function and enhanced glycol ysis in viable but downregulated myocardium, may result from chronic r epetitive ischemia and reperfusion. The present study was conducted to test whether similar trends could be reproduced in an acute animal pr eparation of repetitive stunning. Eight intact pig hearts were extraco rporeally perfused for 115 min and subjected to four cycles of ischemi a [60% decrease in anterior descending flow for 5 min each, interspers ed with 15 min of aerobic reperfusion]. Each bout of ischemia caused a progressive decline in regional systolic shortening such that systoli c shortening was 37% lower at end-reperfusion (P < 0.05 vs. initial co nditions). Regional myocardial O-2 consumption was reduced during isch emia but was not significantly lower at end-reperfusion compared with that under initial conditions. Fatty acid oxidation was unchanged at a ny point during the trials. Although glucose utilization was increased by an average of 264% during the four ischemic periods, it was not si gnificantly or progressively increased during the reperfusion periods. Therefore, although this acute stunning protocol depressed mechanical function, it did not cumulatively increase glycolysis during reperfus ion. This absence of accelerated glycolysis is at variance with the me tabolic findings reported in clinical hibernation and raises concerns regarding this protocol in animal studies designed to simulate short-t erm hibernation.