Limb ischemia preconditions the heart against reperfusion tachyarrhythmia

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Abstract
We investigated the hypothesis that a cardioprotective, antiarrhythmic effect might be obtained by brief ischemia of a remote part of the body before ischemia of the heart. Regional ischemia (RI) was induced in isolated Langendorff-perfused rat hearts: group I, 30-min RI and reperfusion (control hearts; n = 18); group II, 5-min RI before 30-min RI (a reference group of “classic” ischemic preconditioning; n = 12); and group III, ischemic preconditioning with in vivo 10-min limb ischemia (LI) before 30-min RI in the perfused heart ( n = 20). A significant decrease in reperfusion arrhythmia was found in groups II and III compared with group I ( P < 0.02). Release of norepinephrine (NE) and prostacyclin was higher in hearts from animals pretreated with LI ( P < 0.05). Prostacyclin increased in all groups at minute 1 of reperfusion, but there was no correlation to the antiarrhythmic effect. NE increased at the beginning of reperfusion after 30 min of ischemia; this release was significantly diminished after preconditioning with LI ( P < 0.05). We further investigated the role of NE in preconditioning with LI using drug interventions. Pretreatment with exogenous NE protected against tachyarrhythmia. Reserpine given 24 h before LI partially abolished the antiarrhythmic effect of LI preconditioning. However, the α1-adrenoreceptor blocker prazosin did not prevent the effect of LI preconditioning on either ischemic or reperfusion tachyarrhythmia. Therefore, brief ischemia of an extremity protects against reperfusion tachyarrhythmia. One of the humoral mediators involved in this response appears to be NE; others remain to be identified.