THE ABSORPTION OF WATER AND SALT FROM THE SMALL INTESTINE OF THE RAT

Abstract

1. The net absorption rates of water and sodium, measured in vivo in the jejunum and ileum of the rat, were greater from alkaline than from acid solutions, over the pH range 4·4–7·2. 2. Chloride was absorbed more rapidly from the ileum than from the jejunum under all conditions studied. 3. Chloride was absorbed by the ileum from solutions containing between 20–50 mEq/l. less than plasma. Sodium was absorbed by the ileum from isotonic solutions containing between 45–75 mEq/l. less than plasma, but no absorption occurred from hypotonic solutions. 4. The decreasing absorption rates of water from similar solutions containing glucose, urea or mannitol are accounted for in terms of relative osmotic restraint on absorption. 5. The water content of the intestinal wall was found to be linearly related to the dry weight of the segment and to the amount of water absorbed by the segment. About 1·5 per cent of this amount remained in the intestinal wall after two hours circulation. 6. The net uptake of Na and Cl from isotonic fluids and the net entry into hypotonic fluids in jejunal segments were both reduced when mannitol was added to the solutions. 7. With solutions containing 160 mEq/l. sodium in the jejunum, the fluid absorbed was approximately isotonic with that in the lumen. © 1957 The Physiological Society