Remote ischemic preconditioning (RIPC), i.e. brief episodes of ischemia/reperfusion in a remote organ, protects the heart against infarction after myocardial ischemia/reperfusion. However, the transfer of protection from the remote ischemic/reperfused organ to the heart is still not understood. Here we address the transfer of a blood-borne cardioprotective factor from a donor pig undergoing a RIPC protocol and subsequent myocardial ischemia/reperfusion to an isolated perfused recipient rat heart undergoing global ischemia/reperfusion.
Methods: Anesthetized pigs were subjected to either RIPC (4 cycles of 5 min hindlimb occlusion/5 min reperfusion) or placebo. Plasma was separated from arterial blood samples collected 60 min after RIPC or placebo, respectively, and stored at 80°C. Myocardial ischemia was induced by 60 min occlusion of the left anterior descending coronary artery (LAD) with subsequent 180 min reperfusion. The area at risk (AAR) was determined by atrial injection of 5 ml Patentblau after LAD re-ligation at the end of the experiment and infarct size by TTC staining.
Isolated rat hearts were mounted on a Langendorff apparatus and perfused at a pressure of 75 mmHg with Krebs-Henseleit-buffer before undergoing 30 min global ischemia and 120 min reperfusion at 37° C. Pre-warmed pig plasma was added to the Krebs-Henseleit-buffer (1:10) for 8 min before and 5 min after ischemia. Infarct size was determined by TTC staining.
Results: In pigs, infarct size was 47.6±5.5% of the AAR with placebo and 22.1±3.5% with RIPC (mean±SEM; p<0.05; 2-sided t-test). In the isolated rat hearts, perfusate-supplementation with plasma from pigs which underwent RIPC resulted in an infarct size of 25.9±1.9% of the left ventricle as compared to 39.3±2.3% with plasma from pigs of the placebo group (p<0.05). Infarct size in an ischemia/reperfusion protocol without plasma infusion was 42.0±1.2%. The infarct size in isolated recipient rat hearts correlated to that of the donor pigs (r=0.74; n=12).
Conclusion: After RIPC in pigs, a cardioprotective, humoral signal can be transferred to an in vitro bioassay of isolated rat hearts.