Delayed preconditioning prevents ischemia/reperfusion-induced endothelial injury in rats: role of ROS and eNOS.

Ischemic preconditioning (IPC) strongly protects against ischemia/reperfusion (I/R) injury; however, the molecular mechanism involved in delayed preconditioning-induced endothelial protection in peripheral arteries is unknown. Therefore, we examined using functional, morphologic and molecular biologic studies whether delayed IPC decreases formation of reactive oxygen species and upregulates endothelial nitric oxide synthase (eNOS) that in turn contributes to vascular endothelial protection. Adult male Sprague-Dawley rats were subjected to 30-min ischemia induced by mesenteric artery occlusion followed by 60-min reperfusion 24 h after sham surgery or preconditioning (three cycles of 5-min ischemia/5-min reperfusion). Delayed preconditioning prevented the I/R-induced impairment of endothelium-dependent relaxations to acetylcholine (maximal relaxation: sham 91.4±2.2%; I/R 54.0±4.0%; IPC 80.2±6.3%). This protective effect was abolished by NOS inhibitor N(G)-nitro-L-arginine methyl ester and not changed by ascorbic acid. Electron microscopy showed marked endothelial damage after I/R and the ultrastructural changes were prevented by delayed preconditioning. Following I/R, the impairment of eNOS phosphorylation and expression was observed in mesenteric vessels. Furthermore, phosphatidylinositol 3-kinase (PI3K) and Akt phosphorylation were reduced, although total PI3K and Akt remained unchanged. IPC restored I/R-induced impairment of eNOS expression and activity. This was possibly the result of the recovery of PI3K/Akt phosphorylation. Furthermore, I/R increased serum level of malondialdehyde, intravascular superoxide and nitrotyrosine generation, which were abrogated by IPC. These results suggest that delayed preconditioning prevented I/R-induced endothelial injury in peripheral resistance vasculature, both in terms of functional and structural changes. Endothelial protection afforded by delayed IPC is associated with inhibition of oxidative stress and upregulation of PI3K/Akt/eNOS pathway.