Bicarbonate and citrate in oral rehydration therapy: studies in a model of secretory diarrhea.

In situ perfusion of the rat jejunum and ileum was used to study the effect of inclusion of bicarbonate or citrate on the ability of four oral rehydration solutions to promote small-intestinal absorption of water and sodium. Solutions varied in their sodium (60-90 mM) and glucose (111-140 mM) content and osmolality (281-331 mosmol/kg). They were studied before and after exclusion of base both in normal intestine and in secreting intestine after exposure to cholera toxin. All solutions promoted net water absorption in the normal intestine and reversed net water secretion to absorption in the cholera toxin-treated intestine to varying degrees. Net sodium movement was directly related to the sodium content of oral rehydration solutions. Inclusion of bicarbonate or citrate did not promote significantly greater absorption of water or sodium than did solutions without base, in normal or secreting intestine. In the secreting intestine, inclusion of bicarbonate in two solutions actually resulted in greater sodium secretion than did identical solutions from which bicarbonate was omitted. These studies suggest that the inclusion of base or base precursors in oral rehydration solutions to enhance water and sodium absorption is unjustified in both normal and secreting small intestine.