Abstract: 【Abstract】Objective To investigate the protective effect of melatonin (MT) on renal ischemia reperfusion injury and its mechanism in rats. Methods The rat renal ischemia reperfusion model was established by clamping bilateral renal arteries and veins with non-invasive vascular clamp. The rats were then randomly divided into sham operation group, ischemia reperfusion (IR) group, MT 5mg group, MT 10mg group and VC group. Serum BUN and Cr, mitochondrial activity, SOD activity, total ATPase activity, malondialdehyde (MDA) content, nitric oxide (NO) content and eNOS expression in renal tissue, and Bax and Bcl-2 expression levels in renal cortex were detected after reperfusion for 6h and 24h. Results After reperfusion for 6h and 24h and compare to IR group, serum BUN and Cr were significantly decreased in MT 5mg group, MT 10mg group and VC group (for MT 5mg group: t=3.154, P=0.032; t=3.864, P=0.006; t=3.021, P=0.037; t=3.856, P=0.007; for MT 10mg group: t=3.268, P=0.029; t=4.327, P=0.005; t=3.215, P=0.026; t=4.026, P=0.003; for VC group: t=3.415, P=0.014; t=4.586, P＜0.001; t=3.534, P=0.012; t=721, P＜0.001); kidney mitochondrial activity, SOD activity and total ATP activity were significantly increased in MT 5mg group, MT 10mg group and VC group (MT 5mg group: t=1.894, P=0.097; t=0.864, P=0.247; t=16.154, P＜0.001; t=15.587, P＜0.001; t=4.361, P=0.004; t=3.327, P=0.031; MT 10mg group: t=3.762, P=0.016; t=4.143, P=0.008; t=19.637, P＜0.001; t=18.596, P＜0.001; t=5.397, P＜0.001; t=4.832, P＜0.001; VC group: t=3.758, P=0.017; t=3.972, P=0.011; t=18.026, P＜0.001; t=17.923, P＜0.001; t=5.403, P＜0.001; t=4.851, P＜0.001); MDA decreased significantly in MT 5mg group, MT 10mg group and VC group (MT 5mg group: t=4.241, P=0.004; t=5.436, P＜0.001; MT 10mg group: t=5.386, P=0.001; t=6.174, P＜0.001; VC group: t=6.352, P＜0.001; t=6.053, P＜0.001). NO increased significantly in MT 5mg group, MT 10mg group and VC group after reperfusion for 6h as compared that in IR group (MT 5mg group: t=5.821, P＜0.001; MT 10mg group: t=9.107, P＜0.001; VC group: t=8.728, P＜0.001). Conclusions Injection of MT at the early stage of ischemia reperfusion can effectively reduce the mild renal injury and improve renal function in renal ischemia reperfusion injury rats. Its mechanism may relate to the protection of mitochondrial function, the increase of antioxidant enzyme activity, the increase of protective NO content, and the reduction of apoptosis.

Key words: Melatonin, Ischemia reperfusion injury, Kidney, Protection