Clearance of 9-micron spheres and rubidium in the intestinal circulation

Rubidium clearance and 9-micron-sphere entrapment were studied and compared in isolated intestinal preparations under various physiological conditions in 10 dogs anesthetized with intravenous pentobarbital sodium. The chosen intestinal segment was pumped with aortic blood at a constant rate and pressure of about 90-100 mmHg. The temperature of the isolated loop was maintained at 37-38 degrees C with an electrical pad. A mixture of 86Rb and 9-micron-spheres labeled with 141Ce was injected into the arterial cannula supplying the intestinal loop while mesenteric venous blood was collected for activity counting. Three to four intestinal segments were used from each dog. The following three experimental conditions were randomly used for each intestinal segment preparation: 1) a mesenteric venous pressure (MVP) equaling 0 cmH2O and warmed normal saline infused into the lumen of segment; 2) an MVP equaling 0 cmH2O and 5% glucose in saline infused into the intestinal lumen; and 3) the reservoir with venous blood elevated to provide an MVP equaling 17 cmH2O and warmed normal saline infused into the intestinal lumen. A very strong and significant correlation was found between rubidium and microsphere clearances (r = 0.99, P less than 0.0001). Rubidium extraction was inversely associated with blood flow through the intestinal segment (r = 0.49, P = 0.02), while microsphere entrapment (extraction) was independent from intestinal blood flow (r = 0.16). The data suggest that the shunting of 9-micron spheres through tissue reflects the arteriovenous shunting of blood and, therefore, can be used as a tool to study the nutritive and nonnutritive blood flows in tissues.