RESUMEN
To investigate the effect of melatonin on the colon inflammatory injury of rats with colitis and determine whether this effect is associated with inhibition of chemoattractant molecules interleukin [IL-8] and monocyte chemoattractant protein [MCP-1]. The study was designed and implemented in JingMen No.1 People's Hospital, HuBei Province, from May 2006 to April 2007. It involved 72 animals divided into 6 groups of 12 each: normal group, model group, 5-aminosalisalicylic acid group,and melatonin group [dose of 2.5, 5.0, and 10.0mg/kg]. Rat colitis model was established by 2, 4, 6-trinitrobenzene sulfonic acid [TNBS] enema. Interlukin-8 and MCP-1 proteins in colon tissue were examined by immunohistochemistry and western blot. The messenger-RNA expressions of chemokines were determined by reverse transcription polymerase chain reaction analysis. Trinitrobenzene sulfonic acid enema resulted in pronounced pathological changes of colonic mucosa in model rats, which were in accordance with the significantly elevated myeloperoxidase activity. Expressions of chemokines were up-regulated in colitis. Melatonin treatment reduced colonic lesions and improved colitis symptom, and decreased the protein and mRNA expressions of IL-8 and MCP-1 significantly in colon tissues of rats with colitis. Chemokines IL-8 and MCP-1 are elevated in mucosal tissues in colitis and play an important role in the perpetuation of tissue destructive inflammatory processes; melatonin reduces colonic inflammatory injury of rats colitis through down-regulating the expressions of chemokines. Melatonin can be considered as a novel therapeutic alternative for the treatment of inflammatory bowel disease