Vasoactive agents in portal blood during hemorrhagic shock

Abstract

Vasoactive agents released from the intestine during hemorrhagic shock in dogs were studied by perfusing either an isolated terminal loop of ileum or an isolated gracilis muscle with oxygenated portal blood at 100 mm Hg pressure. At 10–20-min intervals femoral arterial blood at 100 mm Hg pressure was used as the perfusate to evaluate changes in the preparation and release of vasoactive agents into the systemic blood supply. By the end of the 40 mm Hg hypotensive period, vasodilators were consistently found in the portal blood. After transfusion of the shed blood, vasoconstrictors usually seen in the arterial blood during the hypovolemic phase were replaced or masked by vasodilators. However, during the remainder of the normotensive period, vascular tone slowly returned to near normal using either source. Terminally, vasodilators were often seen in both arterial and portal blood. Results with muscle were similar to those using an intestinal loop. Although the degree and pattern of vasodilatation do not appear to be adequate to explain the eventual circulatory collapse, it is suggested that the vasodilatation during the last phase of hypovolemic hypotension may be indicative of the release of agents which act on the cardiovascular system to contribute to irreversibility.