Villous motility and unstirred water layers in canine intestine

The possibility that villous motility reduces the mucosal unstirred water layer by mechanical stirring was examined. The frequency of contraction of villi was measured by using videomicroscopic techniques while a segment of anesthetized canine jejunum or ileum with its nerve and blood supply intact was maintained in a sealed chamber through which Tyrode solution was perfused. Radioisotopically labeled inulin, H2O, and butyric and lauric acid were used to measure net and/or unidirectional fluxes from the chamber. The unidirectional absorptive transport of H2O and butyric acid but not lauric acid by jejunal segments was significantly correlated with flow through the chamber. Plasma volume expansion increased villous motility but decreased the absorption of H2O and lauric acid. Absorption of butyric acid from the ileum was little different than from the jejunum although the degree of villous motility was less and net water absorption was greater from the ileum. Absorption of butyric acid into dead tissue indicated that passive diffusion into the tissue accounted for between 7 and 25%, depending on flow rate, of the absorption in intact tissue and that nonspecific binding was low. It was concluded that villous motility did not stir the unstirred water layers and was not directly associated with altered transport.