Remote ischaemic pre- and delayed postconditioning - similar degree of cardioprotection but distinct mechanisms

Abstract

Myocardial ischaemia-reperfusion injury can be significantly reduced by an episode(s) of ischaemia-reperfusion applied prior to or during myocardial ischaemia (MI) to peripheral tissue located at a distance from the heart; this phenomenon is called remote ischaemic conditioning (RIc). Here, we compared the efficacy of RIc in protecting the heart when the RIc stimulus is applied prior to, during and at different time points after MI. A rat model of myocardial ischaemia-reperfusion injury involved 30 min of left coronary artery occlusion followed by 120 min of reperfusion. Remote ischaemic conditioning was induced by 15 min occlusion of femoral arteries and conferred a similar degree of cardioprotection when applied 25 min prior to MI, 10 or 25 min after the onset of MI, or starting 10 min after the onset of reperfusion. These RIc stimuli reduced infarct size by 54, 56, 56 and 48% (all P < 0.001), respectively. Remote ischaemic conditioning applied 30 min into the reperfusion period was ineffective. Activation of sensory nerves by application of capsaicin was effective in establishing cardioprotection only when elicited prior to MI. Vagotomy or denervation of the peripheral ischaemic tissue both completely abolished cardioprotection induced by RIc applied prior to MI. Cardioprotection conferred by delayed remote postconditioning was not affected by either vagotomy or peripheral denervation. These results indicate that RIc confers potent cardioprotection even if applied with a significant delay after the onset of myocardial reperfusion. Cardioprotection by remote preconditioning is critically dependent on afferent innervation of the remote organ and intact parasympathetic activity, while delayed remote postconditioning appears to rely on a different signalling pathway(s).

Figure 1. Cardioprotection conferred by remote ischaemic conditioning applied prior to, during and at different time points after myocardial ischaemia (MI)

A, illustration of the experimental protocols. In all protocols, the model of myocardial ischaemia–reperfusion injury involved 30 min of left coronary artery occlusion followed by 120 min of reperfusion. Remote ischaemic conditioning (RIc) was induced by 15 min occlusion of both femoral arteries. The sham-RIc procedure involved dissection of both femoral arteries without occlusion (arrow). Abbreviations: RPrec, remote preconditioning; RPerc, remote perconditioning; RPerc/Post, remote per-postconditioning; RPost10′, delayed remote postconditioning applied 10 min into reperfusion; and RPost30′, delayed remote postconditioning applied 30 min into reperfusion. B, infarct size is presented as a percentage of the area at risk. Remote ischaemic conditioning confers significant cardioprotection when applied 25 min prior to myocardial ischaemia, 10 or 25 min after the onset of myocardial ischaemia or starting 10 min after the onset of reperfusion. Individual data and means ± SEM are shown. ***P < 0.001. C, images illustrate representative sections of triphenyltetrazolium chloride-stained hearts from all the experimental groups following 30 min ischaemia and 120 min reperfusion.

Figure 2. Activation of sensory nerves supplying peripheral tissue by capsaicin is effective in establishing cardioprotection only when applied prior to myocardial ischaemia

A, illustration of the experimental protocols. Arrow indicates time of subcutaneous administration of capsaicin (3 μg in 10 μl) or vehicle (10% ethanol and 10% Tween 80 in saline; 10 μl) into both hindpaws. B, infarct size is presented as a percentage of the area at risk. Capsaicin application confers significant cardioprotection only when applied prior to myocardial ischaemia. Individual data and means ± SEM are shown. **P < 0.01.

Figure 3. Intact innervation of the remote ischaemic tissue is essential for cardioprotection induced by remote preconditioning but not for delayed remote postconditioning

A, illustration of the experimental protocols. Arrow indicates time of limb denervation by sectioning sciatic and femoral nerves or sham surgery. B, infarct size is presented as a percentage of the area at risk. Denervation of the peripheral ischaemic tissue abolishes cardioprotection induced by remote ischaemic conditioning (RIc) applied prior to myocardial ischaemia, whereas cardioprotection conferred by delayed remote postconditioning (RPost10′) is not affected. Individual data and means ± SEM are shown. ***P < 0.001; n.s., not significant.

Figure 4. Intact parasympathetic activity is essential for cardioprotection induced by remote preconditioning but not by delayed remote postconditioning or direct myocardial preconditioning

A, illustration of the experimental protocols. Arrow indicates time of bilateral vagotomy or sham surgery. B, infarct size is presented as a percentage of the area at risk. Vagotomy abolishes cardioprotection induced by remote ischaemic conditioning (RIc) applied prior to myocardial ischaemia, whereas cardioprotection conferred by delayed remote postconditioning (RPost10′) or myocardial ischaemic preconditioning (IPc) is not affected. Individual data and means ± SEM are shown. ***P < 0.001; n.s., not significant.