Experimental Diarrhea

Abstract

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 HCO 3 transport in the normal and infected small intestine. HCO 3 absorption in the infected ileum was not due to alterations in systemic acid base balance. To explore the mechanism of the luminal disappearance of HCO 3 in the normal rat jejunum and infected rat ileum, changes in luminal solution p H and pCO 2 during intestinal transit were determined with a HCO 3 -free and HCO 3 -containing solutions. The pCO 2 of the HCO 3 -free solution was not altered during transit through the normal or infected intestine suggesting that the tissue pCO 2 was not elevated. However, during perfusion with HCO 3 -containing solutions, from which HCO 3 was being "absorbed", the solution p H decreased and pCO 2 increased significantly in the normal jejunum and in the infected ileum. This is evidence that H secretion was the mechanism of HCO 3 absorption in these segments. The normal rat jejunum was not capable of Na and H 2 O absorption from a HCO 3 -free, 118 mm Na solution, a finding similar to that reported in the human jejunum where a HCO 3 -mediated Na transport mechanism (Na: H exchange) has been proposed.