Endothelial dysfunction of coronary resistance vessels in apoE−/− mice involves NO but not prostacyclin-dependent mechanisms

Objective: We have analyzed the extent of endothelial dysfunction in cardiac resistance vessels of hyperlipidaemic apoE−/− mice and explored whether NO and/or prostacyclin dependent pathways are involved. Methods: Coronary resistance was measured in isolated perfused hearts from WT and apoE−/− mice. To discriminate between NO and PGI2-dependent flow responses, we made use of the finding that acetylcholine (ACh) predominantly activates the prostaglandin pathway whereas bradykinin (Bk) mainly acts via NO in murine cardiac resistance vessels. Results: Basal coronary flow as well as the ACh induced vasodilation (0.1–1 μM) were not different between WT and apoE−/− hearts (flow increase+100%). Similarly, vasodilation in response to the prostacyclin mimetic iloprost reached the same levels. In contrast, the Bk-stimulated [3.3 μM Bk] coronary flow was reduced from 31.6±4.2 in WT to 19.2±2.7 ml min−1 g−1 in apoE−/− hearts. NOS inhibition by ethylisothiourea (ETU, 10 μM) reduced basal as well as Bk-stimulated coronary flow in WT and apoE−/− hearts to the same extent. RT–PCR and Western analysis demonstrated that neither eNOS expression nor protein levels were reduced. Similarly, the flow response to the NO donor SNAP (0.3–33 μM) was not altered suggesting that soluble guanylyl cyclase was not affected. Intracoronary application of superoxide dismutase augmented the Bk-induced vasodilation of apoE−/− hearts almost back to WT levels (26.6±3.3 ml min−1 g−1). In line with this finding the NADPH induced O2− formation was enhanced in cardiac extracts from apoE−/− hearts. Conclusion: apoE−/− hearts develop a hemodynamically relevant endothelial dysfunction at the level of coronary resistance vessels most likely via inactivation of bioavailable NO by superoxide anions. The function of the prostacyclin system is not altered.