Effect of melatonin on the severity of L-arginine-induced experimental acute pancreatitis in rats

Free radicals and lipid peroxidation have an important role in the pathogenesis of the local and systemic inflammation during acute pancreatitis.

The aim of this study was to determine the effect of the free-radical scavenger melatonin on the early phase of experimental acute necrotizing pancreatitis.

Methods: Male Wistar rats were divided in five groups: A (3.2g/kg L-arginine (L-Arg) i.p. twice); MA (50mg/kg melatonin i.p. 30min prior to L-Arg); AM (50mg/kg melatonin i.p. 1h after L-Arg); M (50mg/kg melatonin i.p.); C (physiological saline i.p.). Rats were exsanguinated 24h after the last L-Arg injection.

Results: In groups A, AM and MA L-Arg caused a severe necrotizing pancreatitis confirmed by the significant elevation of serum amylase levels, pancreatic weight/body weight ratio (pw/bw), and pancreatic myeloperoxidase activity vs. groups C. Elevation of the serum amylase level was significantly reduced in group AM vs. group A. The activity of pancreatic antioxidant enzymes [Cu/Zn- SOD, Mn-SOD and catalase (CAT)] was significantly increased. In group MA, the pancreatic CAT activity was significantly reduced vs. A. In group A vs. group C, the lipid peroxidation level, GPx and Cu/Zn-SOD activity were significantly increased in the liver, whereas melatonin pretreatment abolished these changes and decreased the activity of liver CAT vs. group C.

Conclusion: In severe acute pancreatitis a moderate protective effect of melatonin was observed 24h following pancreatitis induction demonstrated by the decrease of serum amylase activity, and lipid peroxidation. Supported by the Hungarian Scientific Research Fund (T042589).