Chronic skeletal muscle ischemia preserves coronary flow in the ischemic rat heart

Abstract

Chronic skeletal muscle ischemia confers cytoprotection to the ventricular myocardium during infarction, but the underlying mechanisms remain unclear. Although neovascularization in the left ventricular myocardium has been proposed as a possible mechanism, the functional capacity of such vessels has not been studied. We examined the effects of chronic limb ischemia on infarct size, coronary blood flow, and left ventricular function after ischemia-reperfusion. Hindlimb ischemia was induced in 65 Wistar rats by excision of the left femoral artery, whereas 65 rats were sham operated. After 4 wk, myocardial infarction was generated by permanent coronary artery ligation. Infarct size was measured 24 h postligation. Left ventricular function was evaluated in isolated hearts after ischemia-reperfusion, 4 wk after limb ischemia. Neovascularization was assessed by immunohistochemistry, and coronary flow was measured under maximum vasodilatation at different perfusion pressures before and after coronary ligation. Infarct size was smaller after limb ischemia compared with controls (24.4 ± 8.1% vs. 46.2 ± 9.5% of the ventricle and 47.6 ± 8.7% vs. 80.1 ± 9.3% of the ischemic area, respectively). Indexes of left ventricular function at the end of reperfusion (divided by baseline values) were improved after limb ischemia (developed pressure: 0.68 ± 0.06 vs. 0.59 ± 0.05, P = 0.008; maximum +dP/dt: 0.70 ± 0.08 vs. 0.59 ± 0.04, P = 0.004; and maximum -dP/dt: 0.86 ± 0.14 vs. 0.72 ± 0.10, P = 0.041). Coronary vessel density was markedly higher (P = 0.00021) in limb ischemic rats. In contrast to controls (F = 5.65, P = 0.00182), where coronary flow decreased, it remained unchanged (F = 1.36, P = 0.28) after ligation in limb ischemic rats. In conclusion, chronic hindlimb ischemia decreases infarct size and attenuates left ventricular dysfunction by increasing coronary collateral vessel density and blood flow.