intestinal ischemia/reperfusion (I/R) leads to bowel impairment via the release of reactive oxygen species (ROS) and neutrophil infiltration. in addition to modulating intestinal integrity, nitric oxide (NO.) inhibits neutrophil activation and scavenges ROS. Attenuated endogenous NO. formation may result in the accrual of these deleterious stimuli. Therefore, we determined nitric oxide synthase (NOS) activity in anesthetized rats subjected to 1 h of superior mesenteric ischemia or ischemia followed by reflow. NOS activity was measured in intestinal tissue homogenates as the conversion rate of H-3-L-arginine to H-3-L-citrulline. Our results demonstrate that intestinal ischemia leads to a decrease in NOS activity indicating lower NO. formation in the animal model. The attenuation in NOS activity was not reversed following 4 h of reperfusion. Western blot analysis revealed that the decline in enzyme activity was accompanied by reduced intestinal NOS HI (endothelial constitutive NOS) expression. These findings provide biochemical evidence for impaired NO. formation machinery in intestinal YR injury.