AIM: To observe the dynamic changes of plasma levels of nitric oxide(NO) and endothelin (ET-1) in portal veins of the rats during prehepatic portal hypertension, and investigate the role of them in hyperdynamic circulation. METHODS: The models of prehepatic portal hypertension were established in Sprague-Dawley rats by means of partial portal vein ligation (PVL). The plasma levels of nitrite/nitrate (NO - 2/NO - 3) and ET-1 in the portal veins were detected by the method of nitric reductase and radioimmunoassay, respectively. In this study, rats were divided into normal, sham operation (SO) and PVL group. SO and PVL rats were divided into several subgroups according to different time after operations. Meanwhile, the changes of several hemodynamic indexes in these rats were also measured. RESULTS: The levels of NO - 2/NO - 3 were significantly increased and ET-1 were significantly decreased in rats at different time after PVL compared with normal control, whereas the hemodynamic indexes changed accordingly. CONCLUSION: The portal hypertensive rats are in hyperdynamic circulatory state (HCS). NO and ET-1 may play an important role in the induction and maintenance of HCS.