Intermittent insulin treatment mimics ischemic postconditioning via MitoKATP channels, ROS, and RISK

Objectives: It has previously been demonstrated that 15-min continuous insulin infusion at immediate reperfusion affords cardioprotection. This study sought to reduce the treatment time of insulin and test if intermittent insulin infusions can mimic ischemic postconditioning.

Design: In a Langendorff perfused rat heart model of regional ischemia, hearts were at the onset of reperfusion subjected to either 5- or 1-min continuous insulin infusion or 3 × 30 s intermittent insulin infusions (InsPost); with or without inhibitors of Akt (SH-6), p70s6-kinase (rapamycin), mitochondrial ATP-sensitive potassium channels (5-hydroxydecanoic acid [5-HD]), or a scavenger of reactive oxygen species (ROS; 2-mercaptopropionyl glycine [MPG]). Infarct size is expressed as percent of area at risk and presented as mean ± standard error of the mean or s.e.m.

Results: Only InsPost was able to reduce infarct size compared with controls (InsPost 33 ± 6% vs. Ctr 52 ± 4%, p < 0.05.). This cardioprotection was abrogated by co-administering SH-6, rapamycin, 5-HD, or MPG. (InsPost + SH-6 56 ± 9%, InsPost + Rapa 55 ± 8%, InsPost + 5-HD 56 ± 7%, InsPost + MPG 60 ± 3% vs. InsPost 33 ± 6% p < 0.05). These results were corroborated by a significant increase in phosphorylated Akt and p70s6k in the InsPost group compared with controls.

Conclusion: Short intermittent insulin infusions can mimic ischemic postconditioning and reduce myocardial infarct size via Akt/p70s6k and mKATP channels/ROS-dependent signaling.