Water absorption and swelling in the rat small intestine in vitro.

Net mucosal-to-serosal water transport and water retention within the tissue were simultaneously measured in the isolated, everted rat jejunum and ileum along with time. The swelling of the epithelium (delta w/DW-delta w/DW-delta v/DW) precedes the absorption of fluid and then it remains contant throughout the experiment. The water uptake, determined as a weight increase, (delta w/DW) and the net water transport determined as a serosal volume increase (delta v/DW) were higher in Krebs-Ringer-bicarbonate than in a Krebs-Ringer-phosphate medium. In the jejunum glucose markedly stimulated both the tissue retention and net transport of water, but such effect was not seen in the ileum. Replacement of chloride with sulphate in the medium diminishes both water transport and retention, but both were markedly stimulated by the addition of glucose to such medium. As a conclusion it seems that during water transport the epithelial layer swells and the swelling increases when the amount of water transported is increased.