Abstract： Objective To evaluate the role of increased portal pressure and portosystemic shunting in elevated level of prostacyclin (PGI2) in portal hypertension.Methods Thirty-six male Sprague-Dawley rats were divided into four groups: prehepatic portal hypertension (PHPH, 8 rats), intrahepatic portal hypertension (IHPH, 9), end-to-side portacaval shunt (PCS, 8), and sham-operated controls (SO, 11). Two weeks after surgery, free portal pressure (FPP) was measured; systemic and splanchnic hemodynamics was studied by radioactive microsphere technique and blood sample from the femoral artery was obtained to measure the level of plasma 6-keto-PGF1 α with radio-immunoassay.Results The FPP (mmHg) in IHPH, PHPH, PCS and SO rats was 13.10±1.02, 12.10±1.52, 3.0±0.82 and 6.86±0.69, respectively. The value of FPP was significantly increased in IHPH, PHPH rats and significantly decreased in PCS rats when compared to SO rats. Cardiac index (CI) and portal venous inflow (PVI) were in the order of PCS>PHPH>IHPH>SO rats. Portosystemic shunting (PSS) in PCS, PHPH, IHPH was 99.7±0.29%, 76.02±20.62% and 30.34±10.18%, respectively. The concentrations of plasma 6-keto-PGF1α (ng/ml) in PHPH, IHPH, PCS and SO rats were 6.93±2.43, 5.09±2.27, 2.36±1.01 and 1.56±0.61, respectively. The concentrations of plasma PGI2 in PHPH, IHPH and PCS rats were significantly higher than those in SO rats. Furthermore, the concentrations of plasma PGI2 in PHPH and IHPH rats were also significantly higher than those in PCS rats. Moreover, a closed positive correlation existed between plasma PGI2 and FPP (r=0.67, P<0.001). Conclusions The results of the present study suggest that the elevated PGI2 in portal hypertension is mainly due to the overproduction of PGI2 in vascular epithelium cells induced by increased portal pressure, whereas portosystemic shunting and liver dysfunction play a secondary role. In addition, the results of this study do not support that PGI2 mediated the hyperhemodynamics in portal hypertension.