Experimental Diarrhea: III. Bicarbonate transport in rat salmonella enterocolitis

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.