AIM: Vasodilatation and increased capillary permeability have been proposed to be involved in the pathogenesis of acute and chronic form of hepatic encephalopathy.Prostacyclin (PGI2) and nitric oxide (NO) are important contributors to hyperdynamic circulation in portal hypertensive states. Our previous study showed that chronic inhibition of NO had detrimental effects on the severity of encephalopathy in thioacetamide (TAA)-treated rats due to aggravation of liver damage. To date, there are no detailed data concing the effects of PGI2 inhibition on the severity of hepatic encephalopathy during fulminant hepatic failure.METHODS: Male Sprague-Dawley rats weighing 300-350 g were used. Fulminant hepatic failure was induced by were divided into two groups to receive intraperitoneal saline (N/S, n = 20) for 5 d, starting 2 d before TAA administration. Severity of encephalopathy was assessed by the counts of motor activity measured with Opto-Varimex animal activity meter. Plasma tumor necrosis factor-α(TNF-α, an index of liver injury) and 6-keto-PGF1α (a metabolite of PGI2) levels were measured by enzyme-linked immunosorbent assay.RESULTS: As compared with N/S-treated rats, the mortality rate was significantly higher in rats receiving indomethacin (20% vs5%, P＜0.01). Inhibition of PGI2 created detrimental effects on total movement counts (indomethacin vs N/S:438±102 vs841±145 counts/30 min, P＜0.05). Rats treated with indomethacin had significant higher plasma levels of TNF-α (indomethacin vsN/S: 22±5 vs 10±1 pg/mL, P＜0.05)and lower plasma levels of 6-keto-PGF1α (P＜0.001), but not total bilirubin or creatinine (P＞0.05), as compared with rats treated with N/S.CONCLUSION: Chronic indomethacin administration has detrimental effects on the severity of encephalopathy in TAA-treated rats and this phenomenon may be attributed to the aggravation of liver injury. This study suggests that PGI2 may provide a protective role in the development of fulminant hepatic failure.