Effect of bicarbonate on efficacy of oral rehydration therapy: studies in an experimental model of secretory diarrhoea.

In situ perfusion of rat intestine was used to evaluate the effect of bicarbonate on the efficacy of a low sodium (35 mmol/l) glucose-electrolyte oral rehydration solution in normal and cholera toxin-treated rat small intestine. In normal intestine, absorption of water was greater (108 (8.1) microliters/min/g; p less than 0.01) and sodium secretion less (-4.3 (0.3) mumol/min/g; p less than 0.01) from the oral rehydration solution containing bicarbonate than from the solution in which bicarbonate was replaced by chloride ions (59.5 (7.2) microliters/min/g and -7.8 (0.8) mumol/min/g, respectively). Glucose absorption in normal intestine was similar with both solutions. In the secreting intestine, both oral rehydration solutions reversed net water secretion to absorption, but inclusion of bicarbonate resulted in significantly less net absorption of both water (2.18 (6.9) microliters/min/g; p less than 0.05) and glucose (18.7 (2.1) mumol/min/g; p less than 0.001) compared with bicarbonate free oral rehydration solution (19.4 (3.9) microliters/min/g and 35.8 (3.7) mumol/min/g, respectively). Net sodium secretion occurred in normal and secreting intestine but was significantly less with the bicarbonate containing oral rehydration solution. These findings suggest that the demonstrable advantage of bicarbonate in promoting water absorption from this oral rehydration solution in normal rat intestine does not apply to cholera toxin treated secreting intestine.