Bicarbonate is absorbed in the ileum of rats with salmonella enterocolitis rather than secreted as in normal animals. In this respect, the infected ileum resembles the normal rat jejunum. This similarity was confirmed by analysis of the relationship of Na to Cl and HCO3 transport in the normal and infected small intestine. HCO3 absorption in the infected ileum was not due to alterations in systemic acid base balance. To explore the mechanism of the luminal disappearance of HCO3 in the normal rat jejunum and infected rat ileum, changes in luminal solution pH and pCO2 during intestinal transit were determined with a HCO3-free and HCO3-containing solutions. The pCO2 of the HCO3-free solution was not altered during transit through the normal or infected intestine suggesting that the tissue pCO2 was not elevated. However, during perfusion with HCO3-containing solutions, from which HCO3 was being “absorbed”, the solution pH decreased and pCO2 increased significantly in the normal jejunum and in the infected ileum. This is evidence that H secretion was the mechanism of HCO3 absorption in these segments. The normal rat jejunum was not capable of Na and H2O absorption from a HCO3-free, 118 mm Na solution, a finding similar to that reported in the human jejunum where a HCO3-mediated Na transport mechanism (Na: H exchange) has been proposed.
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