AIM: To investigate the role of Sonic hedgehog (Shh) on the course of liver ischemia and repeffusion (I/R) in rats,and the interaction between treatment with nitric oxide donor L-Arginine-methyl ester (L-Arg) and up-regulation of Shh expression.METHODS: A total of 30 male Sprague-Dawley rats weighing 220-240 g were used in this study. Sham-control group (G1, n = 10): a sham operation was performed (except for liver I/R). I/R-untreated group (G2,n = 10): rats underwent liver ischemia for 1 h followed by reperfusion for 45 min. I/R-L-Arg group (G3, n =10): after performing the same surgical procedure as in group 2, animals were treated with L-Arg. Liver tissues were taken for determination of malondialdehyde (MDA)levels, and biochemical and histological evaluations were made.RESULTS: Plasma alanine aminotransferase (ALT),aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and γ-glutamyltranspeptidase (GGT) activities were higher in group 2 than in group 3. MDA values and the hepatic injury score decreased in the L-Arg treated group compared to the I/R-untreated group. In group 2,the hepatocytes were swollen with marked vacuolization.Group 3 rats showed well-preserved liver parenchyma,with hepatocytes extending from the central vein. The morphology of the hepatocytes and the sinusoidal structures was normal, without any signs of congestion.Mild Shh positive immunostaining was detected in group 2 animals. The expression of immunoreactive cells was increased markedly in liver tissue from I/R-L-Arg rats.CONCLUSION: Our findings suggest that Shh molecules are critical factors in the pathophysiology of inflammatory liver injury induced by I/R. In addition, NO plays an important role in the immunohistochemical expression of these molecules.