Carbohydrates and purines in underperfused hearts, protected by ischemic preconditioning

Few results, and those controversial, have been published on ischemic preconditioning followed by low-flow ischemia. The aim of this study was to assess whether ischemic preconditioning: (1) confers protection against severe underperfusion; and (2) is mediated by mobilization of proglycogen, resulting in increased anaerobic glycolysis and reduced myocardial injury. Isolated rat hearts were retrogradely perfused and subjected to either 25 min low-flow ischemia (0.6 ml/min) followed by 30 min reperfusion (IC; n=5), or the same protocol preceded by two cycles of 5 min no-flow ischemia and 5 min reperfusion (PC; n=7). Additionally, hearts (n=52) were freeze-clamped at different time points throughout the protocol. Preconditioning improved functional recovery (developed force X heart rate in PC hearts: 54 v 21% in IC hearts; P<0.01) and reduced ischemic damage (cumulative release of creatine kinase during reperfusion: 93 v 215 micro/g dry weight; P<0.05). During ischemia and reperfusion, release of adenosine and the sum of purines was smaller in PC hearts (P<0.05), while lactate release was similar in the two groups. PC reduced both macroglycogen and proglycogen by c. 60% (P<0.01) resulting in constant glycogen levels during low-flow ischemia. In contrast, in IC hearts, both fractions decreased by c. 60% during underperfusion (P<0.01). These results demonstrate that: (1) ischemic preconditioning reduces injury due to severe flow reduction; and (2) preconditioning reduced glycogenolysis without affecting anaerobic glycolysis, suggesting increased glucose uptake.