Capacity of the human colon to absorb fluid

Abstract

To measure the maximum amount of fluid that can be absorbed by the normal human colon, 4 healthy subjects were studied by metabolic balance. When, in addition to normal dietary intakes, 2 liters of isotonic fluid were infused into the cecum each day, fecal weight increased 150% but the frequency of stools increased only slightly. Fecal weight, percentage of water, and frequency increased more when the load of fluid infused into the cecum was 4 liters per day and achieved values found in diarrhea. Under these circumstances, summing the estimated endogenous ileal flow (approximately 2 liters per day) and the infused load, minus the fecal losses, a net maximum absorption of 5700 ml of H2O, 816 mEq of Na, and 44 mEq of K was calculated. In a second set of studies, chenodeoxycholate (approximately 4 g per day) was infused into the cecum, along with a fluid load of 4 liters per day. Water and sodium absorptions were reduced to approximately 5000 ml and 700 mEq, respectively, and diarrhea occurred. Ursodeoxycholate administered in the same way did not alter stool composition or cause diarrhea. Infusion of a single bolus of 250 ml of fluid into the cecum did not alter stool composition; a bolus of 500 ml produced loose stools, Thus, the colon has a surprisingly large capacity to absorb fluid; this capacity is reduced by chenodeoxycholate and is overwhelmed if fluid enters the cecum rapidly. The approach of non-steady state infusions into the cecum may be useful for the study of colonic function and diarrhea.