The permeability of the small intestinal mucosa: A study using iron

Abstract

SUMMARY 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% HCI 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 59Fe 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.There is a continuous passage of substances from the blood out into the intestinal lumen. It has been demonstrated that mucosal permeation rate both in animals and man depends directly upon the plasma concentration of any substance and inversely upon its molecular size (Loehry, Axon, Hilton, Hider, and Creamer, 1970;Loehry, 1973). How these macromolecular substances actually permeate the intestinal mucosa is not fully understood; theoretically it is possible that they pass through epithelial cells, between them, or through gaps left by extruded cells at the tips of the villi. In order to study this further we injected substances into the arterial supply to the small intestine that could be directly visualized in the mucosa. In the present experiments we have used solutions containing iron as the ferric molecule becomes rapidly fixed to various mucosal and connective tissue constituents and is therefore not removed during fixing and staining procedures. MethodsThe experiments were performed on albino rabbits weighing between 2.5 and 3.5 kg under nembutal anaesthesia. The abdomen was opened by a midline incision and loops of small intestine were gently drawn out. Two-inch segments of intestine were clamped off and 0.25 ml of various iron preparations Received for publication 12 June 1973. injected directly into the mesenteric arterial supply to the segment. A biopsy was taken from the segmmnt at a predetermined time interval and the tissue fixed in 10% formalin. No more than four segments were used in each animal and a control was always taken at the end of the experiments from a portion of bowel not used to ensure that there had not been any significant staining from iron that had leaked into the general circulation. In the experiments where the experimental segment was left for more than one minute after injection, the bulldog clamps isolating the segment were removed to prevent ischaemia. The mucosal biopsies were stained with 2% HCl and 2% potassium ferrocyanide for 30 minutes (Perls' Prussian blue reaction) and equal parts of 20 % potassium ferricyanide and 1 % hydrochloric acid for 15 minutes (Turnbull's stain). Experiments were ...

Mechanisms of lipid loss from the small intestinal mucosa.

“…3 By passage between cells: this seems unlikely on anatomical grounds, since the lateral membranes of adjacent cells are fused together near their apices. Although horseradish peroxidase (Hugon and Borgers, 1968) and colloidal iron (Loehry, Parish, and Baker, 1973) can be demonstrated in the intercellular space after parenteral injection, neither substance can be shown to cross the tight junction. However, it is theoretically possible that lipids might enter the lateral membrane from the intercellular space, diffuse along it and leave from the apical membrane without entering the cell, a route proposed for sodium transport in the colon (Edmonds and Pilcher, 1972).…”

Small intestinal permeability in animals and man

“…It is theoretically possible that substances pass between epithelial cells, through them, or through gaps left by extruded cells at the tips of the villi. In fact, all of these routes may be used Warshaw et al, 1971;Hugon and Borgers, 1968;Loehry, Parish, and Baker, 1973). Preliminary results from autoradiographic studies are also in support of this hypothesis (Loehry and Baker, unpublished observations).…”