Absence of Na+–H+ barrier function in mucosa of canine small bowel

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Abstract
The study was designed to determine whether the special Na+–H+ barrier function or the gastric mucosa is present in the mucosa of the small bowel and whether a gastric mucosal barrier breaker (hexanoic acid) would accelerate the fluxes of sodium in duodenum–jejunum and ileum as in the stomach. The observations were made in healthy conscious dogs with Thiry-Vella fistulae of the small bowel or Heidenhain pouches of the gastric corpus. These barrier characteristics of the stomach were completely absent in the small intestine where bidirectional Na fluxes were 5–10 times greater than in the stomach and were not accelerated by hexanoic acid as they were in the stomach.A comparison was made between the rates of absorption of hexanoic acid, sodium hexanoate, and HCl from the pouches and fistulae. The lipid-soluble fatty acid was transported at all sites more rapidly than its water-soluble sodium salt. In the stomach and ileum the H+ of HCl and sodium hexanoate were absorbed at similar slow rates. The duodenal–jejunal mucosa, however, transported H+ at rates nearly identical to those of hexanoic acid. In our tests HCl was not neutralized in duodenal contents while large quantities were neutralized in the contents of ileum.