Noninvasive remote ischemic preconditioning for global protection of skeletal muscle against infarction

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Abstract
The aim of this study was to investigate the efficacy and mechanism of action of a noninvasive remote ischemic preconditioning (IPC) technique for the protection of multiple distant skeletal muscles against ischemic necrosis (infarction). It was observed in the pig that three cycles of 10-min occlusion and reperfusion in a hindlimb by tourniquet application reduced the infarction of latissimus dorsi (LD), gracilis (GC), and rectus abdominis (RA) muscle flaps by 55%, 60%, and 55%, respectively, compared with their corresponding control ( n = 6, P < 0.01) when they were subsequently subjected to 4 h of ischemia and 48 h of reperfusion. This infarct-protective effect of remote IPC in LD muscle flaps was abolished by an intravenous bolus injection of the nonselective opioid receptor antagonist naloxone (3 mg/kg) 10 min before remote IPC and a continuous intravenous infusion (3 mg/kg) during remote IPC and by an intravenous bolus injection of the selective δ1-opioid receptor antagonist 7-benzylidenealtrexone maleate (3 mg/kg). However, this infarct-protective effect of remote IPC was not affected by an intravenous bolus injection of the ganglionic blocker hexamethonium chloride (20 mg/kg) or the nonspecific adenosine receptor antagonist 8-( p -sulfophenyl)theophylline (10 mg/kg) or by a local intra-arterial injection of the adenosine1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (3 mg/muscle flap) given 10 min before remote IPC. It was also observed that this remote IPC of skeletal muscle against infarction was associated with a slower rate of muscle ATP depletion during the 4 h of sustained ischemia and a reduced muscle neutrophilic myeloperoxidase activity after 1.5 h of reperfusion. These observations led us to speculate that noninvasive remote IPC by brief cycles of occlusion and reperfusion in a pig hindlimb is effective in global protection of skeletal muscle against infarction. This infarct-protective effect is most likely triggered by the activation of opioid receptors in the skeletal muscle, and remote IPC is associated with an energy-sparing effect during sustained ischemia and attenuation of neutrophil accumulation during reperfusion.