It is well recognized that vascular sensitivity and vascular tone were reduced in portal hypertension. In this study, vascular responsiveness to norepinephrine (NE) and endogenous vasoconstrictor tone were assessed in each level of portal hypertensive intestinal microcirculation. Methods: The intestine of normal and prehepatic portal hypertensive rats were prepared forin vivo microscopic observation and 1st, 2nd or 3rd order arteriole (1A, 2A, 3A) was selected for study. Diameter and red cell velocity were continuously monitored and used to calculate blood flow. Once baseline blood flow was obtained, the preparation was exposed to several concentrations of NE for dose-response curve, and antagonists against vasopressin (VP), angiotensin II (AII) or ad-renergic receptors (α).Conclusions: 1. Intestinal microvascular responsiveness to NE was reduced in portal hypertension, which was mainly due to abnormalities in terminal arterioles. 2. Major changes in vasoregulatory control occur in portal hypertensive intestinal microcirculation. 3. These changes may partly explain hemodynamic abnormalities in portal hypertension.