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AIM: To evaluate the effect of tumor necrosis factor (TNF),endothelin (ET) and nitric oxide (NO) on hyperdynamic circulation (HC) of rats with acute and chronic portal hypertension(PHT).METHODS: Chronic portal hypertension was induced in Wistar rats by injection of carbon tetrachloride. After two weeks of cirrhosis formation, L-NMMA (25 mg/kg) was injected into one group of cirrhotic rats via femoral vein and the experiment was begun immediately. Another group of cirrhotic rats was injected with anti-rat TNFa(300 mg/kg)via abdominal cavity twice within 48 h and the experiment was performed 24 h after the second injection. The blood concentrations of TNFc, ET-1 and NO in portal vein and the nitric oxide synthase (NOS) activity in hepatic tissue were determined pre-and post-injection of anti-rat TNFa or LNMMA. Stroke volume (SV), cardiac output (CO), portal pressure (PP), superior mesenteric artery blood flow (SMA flow) and lilac artery blood flow (IAflow) were measured simultaneously. Acute portal hypertension was established in Wistar rats by partial portal-vein ligation (PVL). The parameters mentioned above were determined at 0.5 h,24 h, 48 h, 72 h and 120 h after PVL. After the formation of stable PHT, the PVL rats were injected with anti-rat TNFa or L-NMMA according to different groups, the parameters mentioned above were also determined.RESULTS: In cirrhotic rats, the blood levels of TNFa, NO in portal vein and the liver NOS activity were significantly increased (P＜0.05) while the blood level of ET-1 was not statistically different (P＞0.05) from the control animals (477.67±83.81 pg/mL vS48.87±32.79 pg/mL, 278.41±20.11 μmol/L vs 113.28±14.51 μmol/L, 1.81±0.06 u/mg.prot vs 0.87±0.03 u/mg.prot and 14.33±4.42 pg/mL vs 8.72±0.79 pg/mL, respectively). After injection of anti-rat TNFa,the blood level of TNFa was lower than that in controls (15.17±18.79 pg/mL vs48.87±32.79 pg/mL). The blood level of NO and the liver NOS activity were significantly decreased, but still higher than those of the controls. The blood level of ET-1 was not significantly changed. PP, SV,CO, SMAfiow and IAfiow were ameliorated. After injection of L-NMMA, the blood level of NO and the liver NOS activity were recovered to those of the controls. PP and CO were also recovered to those of the controls. SV, SMAflow and IAfiow were ameliorated. In PVL rats, the blood levels of TNFa, NO in portal vein and the liver NOS activity were gradually increased and reached the highest levels at 48 h after PVL. The blood level of ET-1 among different staged animals was not significantly different from the control animals. PP among different staged animals (2.4±0.18 kPa at 0.5 h, 1.56±0.08 kPa at 24 h, 1.74±0.1 kPa at 48 h,2.38±0.05 kPa at 72 h, 2.39±0.16 kPa at 120 h) was significantly higher than that in controls (0.9±0.16 kPa). After injection of anti-ratTNFa in 72 h PVL rats, the blood level of TNFa was lower than that in controls (14±14 pg/mL vS 48.87±32.79 pg/mL). The blood level of NO and the liver NOS activity were significantly decreased, but still higher than those of the controls. The blood level of ET-1 was not significantly changed. PP was decreased from 2.38±0.05 kPa to 1.68±0.12 kPa, but significantly higher than that in controls. SV, CO, SMAflow and IAflow were ameliorated.After injection of L-NMMA in 72 h PVL rats, the blood level of NO and the liver NOS activity were recovered to those of the controls. PP, SV, CO, SMAflow and IAfiow were also recovered to those of the controls.CONCLUSION: NO plays a critical role in the development and maintenance of HC in acute PHT and is a key factor for maintenance of HC in chronic PHT. TNFa may not participate in the hemodynamic changes of HC directly, while play an indirect role by inducing the production of NO through activating NOS. No evidence that circulating ET-1 plays a role in both models of portal hypertension has been found.