The permeability of the small intestinal mucosa: a study using iron.

Various substances containing iron were injected into the lumen of the small intestine in rabbits and into the mesenteric arterial supply. Sections of the mucosa were stained for ferric ions by immersing for 30 minutes into equal parts of 2% HCl and 2% potassium ferrocyanide (Prussian Blue reaction). The ferric ion is bound to various cell structures and its passage through the mucosa could therefore be demonstrated. Iron appeared to pass from the blood into epithelial cells, especially near the tips of the villi, and also between cells as far as the junctional membrane. Studies using (59)Fe demonstrated the rapidity of transfer of iron from the blood into the intestinal lumen. After a period of ischaemia epithelial cells in other situations also appeared permeable to iron. The implications of the loss of substances from the blood into the lumen by these routes is discussed.