Canine intestinal transit and digestion of radiolabeled liver particles

Using conscious dogs with chronic gastrointestinal fistulas, we studied the intestinal transit of radiolabeled liver particles relative to the transit of a liquid phase marker, polyethylene glycol. All studies were performed during a "fed" intestinal motility pattern induced by feeding or by intestinal perfusion with a fat-containing solution. Median transit times were determined from duodenum to fistulas at the midintestine, or at the terminal ileum, by recovery of polyethylene glycol and radiolabel in effluent from the fistulas. We also sized recovered particles of liver to determine the extent of digestion or fragmentation, or both, in transit. After a steak meal, when liquid flows were very low, the liquid marker and small (0.5-0.7 mm) and large (2-3 mm) particles moved through the proximal intestine together at a slow rate. When intestinal liquid flows were progressively increased from 2 to 24 ml/min by intestinal perfusion, transit was progressively accelerated; but 2-mm particles moved at 25%-20% of the rate of polyethylene glycol or 0.5-mm particles. Increasing transit with increasing flows was associated with decreasing digestion or fragmentation of liver particles. Under most conditions, 2-mm particles were well digested or fragmented than 0.5-mm particles. We conclude that fluid flows have a major effect on transit and digestion of food particles in the small intestine.