The mechanism of decreased intestinal sodium and water absorption after acute volume expansion in the rat

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Abstract

Studies were performed in rat small intestine in vivo to determine the effect of saline infusion on intestinal transport of Na+ and H2O. Saline infusion decreased net Na+ flux (JnNa) from 12.7 ±0.8 to 6.4 ±1.5 μEq/hr per cm in the jejunum when the intestinal perfusate contained both Na+ and glucose. A similar fall in JnNa occurred in ileum. When mannitol was substituted for glucose in the perfusate, control absorption decreased 29% in jejunum and 18% in ileum, but saline infusion still caused a decrease in JnNa quantitatively similar to that seen when glucose was present. When choline was substituted for Na+ in the perfusate, there was net movement of Na+ from blood to lumen during control and this net secretion was increased further after saline infusion. These observations suggest that saline infusion has a similar effect to decrease intestinal JnNa under three widely different conditions of basal sodium transport. Permeability of intestinal mucosa to inulin was very low under basal conditions but increased fivefold after saline infusion, and the unidirectional flux of Na+ from blood to lumen doubled. This increase in unidirectional flux of Na+ was greater than the observed decrease in JnNa.

Authors

Michael H. Humphreys, Laurence E. Earley