BACKGROUNDCyclooxygenase (COX) is the rate-limiting enzyme in the production of prostanoids from arachidonic acid. COX-2 is the inducible enzyme in the COX family, together with the prostanoids forms the COX-2/prostanoid pathway. Research showed that the COX-2/prostanoid pathway is activated in hepatic diseases and liver stress reaction, such as fibrogenesis, portal hypertension, carcinogenesis, and ischemic/reperfusion injury. But there was no report on visceral pain induced liver stress. This study was to investigate the role of the COX-2/prostanoid pathway in liver stress response in rat acute colitis visceral pain liver stress model.

METHODSFifty-three male SD rats were randomly divided into Naive, Model, NS398 treatment, and Morphine treatment groups. The rat acute colitis visceral pain liver stress model was established under anesthesia by the colonic administration of 0.5 ml of 6% acetic acid using a urethral catheter. NS398 and morphine were administrated 30 minutes prior to model establishment in NS398 and Morphine treatment groups respectively. Spontaneous activities and pain behavior were counted and the extent of colonic inflammation was assessed histologically. Liver tissue levels of Glutathione-S-Transferase (GST) activity, COX-2 mRNA, prostaglandin E2 (PGE2), thromboxane B2 (TXB2) and 6-Ketone-prostaglandin F1alpha (6-K-PGF1alpha) contents were assessed.

RESULTSThirty minutes after the colonic administration of acetic acid, a significant decrease in spontaneous activities and an increase in pain behaviors were observed in Model group (P < 0.01 and P < 0.05 respectively), accompanied by colonic inflammation. Liver GST activity levels significantly dropped (P < 0.05). Liver COX-2 mRNA expression significantly increased, accompanied by an increase in liver concentrations of PGE2 and TXB2, but no obvious change in 6-K-PGF1alpha concentrations. NS398 and morphine both ameliorated post-stress liver GST activity (P < 0.05 and P < 0.01 respectively), decreased stress-induced COX-2 expression, decreased PGE2 and TXB2 production, but increased liver 6-K-PGF1alpha levels. Morphine attenuation in colonic tissue inflammation was apparent at 24 hours (P < 0.05).

CONCLUSIONSAcute colitis visceral pain liver stress can induce liver injury. Liver injury might have occurred through the activation of the COX-2/prostanoid pathway and increased production of PGE2 and TXB2. Effective analgesia might offer protective effect during visceral pain stress.