An investigation of small intestinal electrolyte transport was performed in a subject with congenital chloridorrhoea using a constant perfusion technique. The results indicate that the diarrhoea was not due to an abnormally high rate of secretion of fluid into the duodenum, and transport of electrolytes and glucose was normal in the jejunum. In contrast there was a marked abnormality of electrolyte transport in the ileum, chloride, sodium, and water entering the lumen and bicarbonate being absorbed in the absence of any concentration gradients for these ions. This is clearly different from the finding in normal subjects of sodium chloride and water absorption and bicarbonate secretion.
It is suggested that the likely prime mechanism for these abnormalities is a chloride/bicarbonate exchange acting in the direction of chloride secretion, that is, in the opposite direction to the normal anion exchange. The hydrogen ion gradient set up by this exchange could have induced a secondary reversal of the normal sodium/hydrogen exchange so that hydrogen was absorbed and sodium secreted.
From an analysis of the stool electrolyte concentrations and the rectal electrical potential difference it is suggested that in the colon chloride was secreted and bicarbonate absorbed against electrochemical gradients. Here too a reversed chloride/bicarbonate exchange is possibly responsible for the composition of the faecal electrolytes. As evidenced by the low faecal sodium concentration and the normal rectal potential difference, sodium transport is probably normal in the colon.
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