['The present study examined the effects of intraportal infusion of L-arginine on ischemia/reperfusion injury (I/RI) in pig livers, by observing changes in the liver function, liver cell morphology, and changes in the mitochondrial ultrastructure.', 'The involvement of the nitric oxide (NO) pathway in the reperfusion-ischemic phenomenon is complex and not fully understood. Likewise, little is known about the possible benefit of intraportal infusion of L-arginine (substrate for the NO synthesis) on liver I/RI.', 'A pig model consisting of 90 min of hepatic ischemia and 180 min of reperfusion was employed. Eighteen female hybrid pigs were randomly divided into three groups: sham-operated, non-preconditioned, and pharmacologically preconditioned group (intraportal infusion of L-arginine 400 mg/kg) 10 min before being subjected to ischemia and reperfusion. Serum concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), thiobarbituric acid reactive substances (TBARS), and the bile flow were measured. Liver biopsies were taken 180 min after reperfusion for histology, caspase-3 immunohistochemistry, and ultrastructural examination of mitochondria.', 'In the pharmacologically preconditioned group, we observed increased bile flow (P < 0.01) and improved serum AST levels (P < 0.01) relative to the non-preconditioned group. Serum concentrations of TBARS did not differ between the groups. Sinusoidal congestion (P = 0.02) was more evident in the non-preconditioned group than in the sham operated group. Infiltrating PMNs (P = 0.01) were more evident in the non-preconditioned group than in the sham and pharmacologically preconditioned group. The pharmacologically preconditioned group showed an approximately 2.5-fold decrease in caspase-3 activity relative to the non-preconditioned group (P < 0.01). Notably, damage to the mitochondrial ultrastructure in the pharmacologically preconditioned group was reduced relative to the other groups (P < 0.01).'] Does pharmacological preconditioning using intraportal infusion of L-arginine protect against hepatic ischemia reperfusion injury?