Background
Preconditioning (PreC) and postconditioning (PostC) reduce infarct size. We sought to determine the effects of PreC and PostC, alone or in combination, on infarct size and expression of intracellular signals in different ischemia models.
Methods
Male rabbits were subjected to myocardial ischemia followed by 3-hour reperfusion. In a first series we applied 3 ischemia models [a 20-min period (20), a 40-min period (40), and two sequential 20-min periods (20-20)] and 3 types of interventions [no intervention (controls, C), 2 cycles of 5-min ischemia/10-min reperfusion before index ischemia (PreC) and 6 cycles of 10-s ischemia/10-s reperfusion after index ischemia and/or between the sequential ischemic periods (PostC)] (12 groups in total). Infarct size (I) and area at risk (R) were assessed ( % I/R). In a second series, samples were taken for western blot analysis of Akt phosphorylation.
Results
Overall, % I/R differed significantly among groups (p < 0.001). In control groups, C-40 had a greater % I/R than C-20 (p = 0.006). In intervention groups, no differences were found in % I/R. All intervention groups had significantly lower % I/R compared to C-40 group (p < 0.001), whereas, compared to C-20-20 group, PreC-20-20, 20-PostC-20, 20-PostC-20-PostC and PreC-20-20-PostC groups had lower % I/R (all p < 0.05). Akt was increased in all groups in which a significant % I/R reduction was achieved (p < 0.05 versus all other groups).
Conclusions
PreC and PostC, alone or in combination, are effective when an ischemic insult of a given duration is applied either as a single or as sequential periods. Protection from either intervention is associated with an enhanced Akt activation.
