Heparin prevents postischemic endothelial cell dysfunction by a mechanism independent of its anticoagulant activity

Heparin may have protective effects on postischemic vascular endothelial cell function that are distinct from its anticoagulant, antiplatelet, or anticomplement activity. We tested this hypothesis in isolated rat hindlimbs.

Isolated rat hindlimbs underwent 60 minutes of normothermic ischemia and 10 minutes of reperfusion. Potential heparin interaction with plasma-based proteins or cells was eliminated by perfusion of the hindlimbs with a nonrecirculated albumin-enriched crystalloid buffer. Endothelial function was assessed by measurement of endothelium-derived relaxing factor (EDRF) activity. Limbs perfused at constant pressure were subjected to increasing log dose infusions of acetylcholine and nitroprusside to measure endothelial-dependent (EDRF-mediated) and endothelial-independent vasoreactivity, respectively. Fifty limbs were divided into seven groups: two nonischemic groups (one with heparin) and five ischemia/reperfusion groups treated with increasing doses of heparin (0 to 1.0 U/ml perfusate).

The nontreated ischemia/reperfusion group (n = 12) had a 46.2% reduction in endothelial-dependent vasodilation of the rat hindlimb when compared with the nonischemic control (n = 7, p < 0.05). Treatment with heparin 0.5 U/ml (n = 6) nearly abolished this attenuation of endothelial-dependent vasodilation (4.3% reduction, p = not significant vs nonischemic control). The endothelial protective effect of heparin was dose-dependent: groups treated with 0.25 U/ml (n = 6) and 0.1 U/ml heparin (n = 7) showed progressive impairment in postischemic EDRF-mediated vasodilation. Endothelial-independent vasodilation induced by nitroprusside was unchanged by ischemia/reperfusion or heparin treatment, which confirmed that the postischemic damage and its protection by heparin were specific to the endothelium.

Heparin prevented postischemic endothelial cell dysfunction by a mechanism independent of its interactions with plasma-based proteins or cells. This nonanticoagulant protective effect may contribute to the salutary effects of heparinization during acute ischemic events.