Methods

Measurement of osmotic flow of water. The movement of water into the intestinal lumen in response to hyper-tonic solutions of urea, erythritol, and sodium chloride was compared in a given gut segment to that induced by solutions of mannitol ofthe same tonicity; these comparative studies were performed at different levels of the small intestine of 20 normal male and female sub-jects between the ages of 21 and 40. The net water move-ment into the gut lumen was measured by the dilution of a nonabsorbable marker, a technique that has been previously validated (7-9). Subjects were intubated with a triple-lumen polyvinyl tube prepared by fusing single tubes with tetrahydrofuran. The opening of the tube used for infusion of the test solutions was 10 and 30 cm proximal to that of the two collecting tubes. The internal diameter of the infusion tube was 0.7 mm; that of the collecting tubes was 1.8 mm. A 2-cm piece of 16F polyvinyl tubing containing multiple small holes (no larger than 1.8 mm) was attached to the opening of each collecting tube to facili-tate drainage. The location of the tube was determined fluoroscopically after contrast material had been injected into the tube with the most distal opening, and was ex-pressed as the length of tubing between the incisor teeth and the infusion point when slack had been removed from the portion of the tube that was in the stomach. Expressed in this way, the pylorus is approximately 60, the ligament of Treitz 90, and the ileocecal valve 350 cm from the teeth.