Studies on diffusion through surviving isolated intestine

Abstract

THE process of absorption of soluble substances from the intestine has generally been investigated by determining either the amount of substance which disappears in a given time after placing the solution in an isolated or T hiry Vella loop in the living animal, or its concentration in the absorbing fluid. On account of the obvious difficulties, both experimental and chemical, standing in the way of successful application of the latter method, when the blood of the portal vein is used, we have sought for some other means by which the behaviour of absorbed substances might be studied, and the present paper embodies the results.Diffusion is allowed to occur through the walls of isolated portions of intestine kept alive in a bath of oxygenated saline solution at body temperature. We shall show that under such conditions there is distinct evidence of selective absorption, and that this cannot be explained by known physico-chemical laws. Since there is no blood supply in the walls of the gut under these conditions and since, as Co ri, C ori and G olt z(1) have shown, soluble substances are absorbed from the peritoneal cavity in obedience to physico-chemical laws, it seems permissible to assume that the selective property is a function of the mucous membrane. We were led to the use of this method through the observation, made by one of us (H. E. M.) in association with Southgate(2), that the movements of isolated pieces of intestine are but little affected by marked changes in the chemical composition or the H-ion concentration of solutions placed in the lumen, whereas, as is well known, they are extremely sensitive to changes in the outer fluid. These workers also showed that destruction of the vitality of the lining epithelium, by preliminary treatment with weak sodium fluoride solution, increased the permeability so that the movements became immediately susceptible to the influence of solutions placed in the lumen.

The absorption of glucose from the alimentary canal

“…PREVIOUS work on the absorption of sugars has shown that the rate of transference of glucose from solutions placed in the lumen of surviving segments of intestine into the outer saline environment is at a maximum at 0*75M concentration [Auchinachie, Macleod and Magee, 1930;Macleod, Magee and Purves, 1930]. In order to investigate the full significance of this optimal concentration it was considered desirable to test its applicability to the living animal.…”

Selective absorption of carbohydrates

“…WE have shown [Auchinachie, Macleod and Magee, 1930] that certain solutes pass from the lumen of surviving segments of mammalian intestine into the outer nutrient fluid at body temperature in a manner indicating some degree of persistence of selective action in the intestinal wall, located probably in the epithelial cells [Magee, 1930]. We have also demonstrated that there is an optimal concentration of glucose, 3M/4, at which diffusion occurs most rapidly under these conditions.…”

“…In the experiments of the present series our technique as previously described [Auchinachie, Macleod and Magee, 1930] has been modified so as to prevent any appreciable fall in temperature of the segments during their removal from the animal. The abdomen was opened in a warm bath of Tyrode, the intestine washed out gently with warm normal saline and segments of equal length measured, excised and fastened on the tubes while still submerged.…”

The absorption of monosaccharides from the large intestine of the rat under urethane anaesthesia

“…We have therefore concluded that no loss of sugar by bacterial action in the loops is to be expected under our conditions. Although the large intestine in the living animal was almost impermeable to glucose, when it was filled with glucose solution and suspended in a bath of warm Ringer solution, according to the method of Auchinachie, Macleod & Magee [1930], a certain amount of glucose passed through into the surrounding fluid.…”