Comparative duodenal, jejunal and ileal responses to luminal saline load.

Intestinal ionic exchanges were studied in rat duodenal, jejunal and ileal ligated loops in response to different luminal saline loads: NaCl concentration varied from 150-0 mM, solutions being made isoosmotic with mannitol. The contact delay was 60 min. An exponential relationship was found between water, Na and Cl movements and the initial saline concentration. Maximal absorption was obtained with 150 mM NaCl, and was significantly higher in the duodenum than in the jejunum and ileum. The NaCl concentration for which water, Na, and Cl movements were null was approximately 70 mM NaCl in the duodenum and jejunum, 41 mM for Na and 18 mM for Cl in the ileum. The water efflux induced by the 0-mM NaCl test solution was maximal in the duodenum (1.5 +/- 0.2 ml/h) and decreased in the jejunum (0.8 +/- 0.1 ml/h) and ileum (0.3 +/- 0.1 ml/h) as did sodium, chloride and non-chloride anion efflux. These data support the functional heterogeneity of the small intestine regulating the water and ion exchange in response to luminal saline load, the main difference being connected with the efflux capacity of the mucosa, decreasing from the duodenum to the jejunum and ileum.