Small intestinal permeability. 1. Effects of ischaemia and exposure to acetyl salicylate.

Permeability of the small intestinal mucosa was estimated using a perfusion technique after either a period of ischaemia or exposure to acetyl salicylate. It was shown that these procedures increased the passive permeability of the mucosa to macromolecules while maintaining normal mucosal selectivity. Histologically, there was derangment of the epithelial cell layer of the villous tips without damage to the epithelial basement membrane or subepithelial structures. It is concluded that the epithelial cell layer is purely limiting with no selective function and that the role of selectivity must be ascribed to either or both of the other mucosal barriers, the capillary and the epithelial basement membrane.