Maximal capacity for fluid absorption in human bowel.

The intestinal handling of fluid has been studied in ten healthy volunteers while an isotonic saline solution (NaCl 140 mM, KC1 5 mM) was perfused into the stomach at rates of 5, 10, 15, and 20 ml/min. Polyethylene glycol 4000 (PEG-4000), as a nonabsorbable marker, was infused into the second portion of duodenum, and the intestinal contents were sampled continuously at a steady rate at 25, 50, 155, and 180 cm distally. Radiological assessment showed that the proximal sampling point was located at the angle of Treitz when the distal site was usually in the terminal ileum. Stools were collected for the following 12 hr. Volumes sampled from each site were used as a correction for volumes calculated at each distal site. The absorption rates of water (0.035 ml), sodium (4.72 muEq), and potassium ((0.18 183 muEq) per minute and per centimeter of bowel were constant along the small intestine and were independent of the perfusion rate. Stools only appeared when terminal ileal input to the colon was above 6 ml/min. When this occurred, the net absorption of water by the colon was 2.7 +/- 0.3 ml/min whatever the rate fluid entered the colon. A significant positive correlation was observed between ileal outputs and volume of stools.