Protective effect of ischemic preconditioning on retinal ischemia-reperfusion injury in rats

Abstract

Background: A short period of ischemia can induce remarkable tissue resistance to the deleterious effects of subsequent ischemia and reperfusion. We performed a study to investigate the effect of ischemic preconditioning on retinal ischemia-reperfusion injury in rats. Methods: Ten Wistar albino rats were divided into two groups of five animals (10 eyes): one group underwent 5 minutes of ischemic preconditioning (achieved by clamping the common carotid arteries at the time of vertebral artery cauterization), and the other did not (control group). In both groups, the vertebral arteries were occluded bilaterally with an electric needle coagulator under an operating microscope. Forty-eight hours later the rats were reanesthesized, and both common carotid arteries were clamped to interrupt blood flow. The duration of ischemia was 30 minutes. The clamp was then removed to enable reperfusion for 4 hours. The animals were killed by decapitation, and retinal sections were evaluated under light and electron microscopy. The signs of ischemia-reperfusion injury (cellular degeneration, vacuolization between retinal layers, increase in retinal thickness due to edema, mononuclear cell infiltration and apoptotic cell count) were recorded. Results: Light microscopy of retinal sections from rats in the ischemic preconditioning group showed a well-preserved retinal structure. The mean thickness values (and standard deviation [SD]) for the inner nuclear layer (104.0 µm [2.54 µm] vs. 49.0 µm [10.83 µm]) and inner plexiform layer (134.8 µm [10.13 µm] vs. 88.5 µm [17.46 µm]) were significantly higher in the control group than in the preconditioning group (p = 0.009), indicating increased retinal thickness in the former group due to tissue edema resulting from ischemia-reperfusion injury. The mean mononuclear cell count (6.67 [SD 1.97] vs. 2.5 [SD 1.0]) and apoptotic cell count (18.2 [SD 5.7] vs. 5.3 [SD 1.0]) were significantly higher in the control group than in the preconditioning group (p = 0.002), indicating an inhibitory effect of ischemic preconditioning on leukocyte infiltration and apoptotic cell death. Interpretation: Ischemic preconditioning attenuated ischemia-reperfusion injury in the rat retina.