Vascular responsiveness in obstructed gut. Multiorgan system failure due to hypotension and sepsis is an important cause of death in patients with bowel obstruction. We have investigated the pathophysiology of this entity in an animal model. After 5 days of bowel obstruction, blood flow in the superior mesenteric artery was measured with and without Pitressin and norepinephrine given in separate experiments. In controls, Pitressin in moderate dosages caused a substantial fall in gut blood flow, which was not seen in obstructed animals (blood flow reduction 52 percent vs. 11 percent in sham and obstructed animals respectively, P less than 0.01). Similarly, norepinephrine infusion had less of an effect on gut blood flow in obstructed animals (blood flow reduction 79 percent vs. 58 percent sham vs. obstructed animals (P less than 0.05). Thus, both agents had dose-related effects on gut blood flow, which was maintained at a higher level throughout the drug infusion periods in the bowel of obstructed animals, demonstrating that splanchnic flow is less responsive to vasoactive drug infusion under these experimental conditions. Because splanchnic vasoconstriction is an important feature of normal hemodynamic homeostasis, we suggest that these results may help explain some aspects of the pathophysiology of multiorgan failure caused or worsened by systemic hypotension seen in bowel obstruction. 