Small intestinal fluid absorption in the rat during haemorrhage and its importance for plasma refill.

Small intestinal net fluid absorption and its importance for plasma volume restitution during a slow, stepwise haemorrhage was studied in rats. A continuous administration of a Krebs-glucose solution into the intestinal lumen increased the tolerated maximal bleeding volume from 31 to 70% of initial total blood volume. The 'small intestinal' autotransfusion rate, i.e. the rate of fluid mobilized from the intestinal lumen into the vascular compartment, was calculated to 2.3 ml h-1 100 cm-2 small intestinal serosal surface. 'Small intestinal' autotransfusion is proposed to be an important mechanism in the defence line against hypovolaemia. Haemorrhage induced a 40% increase in small intestinal net fluid absorption. This increase was abolished after pretreatment with Captopril, an angiotensin-converting enzyme blocker. Post-ganglionic denervation of the small intestine reduced, but did not abolish, the stimulatory effect of haemorrhage on net fluid absorption. These results indicate that both a direct nervous component and the renin-angiotensin system are of importance for the increase in small intestinal net fluid absorption observed after haemorrhage.