SUMMARY1. A new technique has been developed for making serial measurements of water and solute absorption from the lumen of isolated small intestine.2. The isolated intestine is perfused in a single pass with a segmented flow of slugs of liquid separated by bubbles of oxygen-carbon dioxide mixture. Simultaneous collections are made of effluent from the lumen and of the fluid which is transported across the mucosa. This latter fluid appears to be a fair sample of the tissue fluid.3. Conditions in the lumen can be changed within less than 5 min. The effects of two or more treatments applied to the same segment of intestine can be determined and the time course of a change in luminal conditions.4. The rate of appearance of solutes on the serosal side depends on the rate of water absorption, and changes exponentially towards a steady state. The rate constant is a function of tissue fluid volume.5. In the steady state the concentration of glucose in the tissue fluid is 71 mm when the luminal concentration is 28 mm, and is 45 mM when the luminal concentration is 8-3 mM.6. For solutes such as glucose for which reflux from tissue fluid to lumen is small relative to flux from lumen to tissue fluid, the time of attainment of a steady state in secretion is usually 50-60 min.7. For solutes such as sodium for which the reflux is relatively high, the steady state may be reached in 15-20 min.8. The Km for glucose absorption (14-19 mM) is much lower than is found with unsegmented flow perfusion.9. These findings emphasize problems in interpreting results from other types of intestinal preparation.10. The rate of glucose absorption from the lumen falls only gradually when the luminal sodium concentration is reduced abruptly. In contrast

Despite the physiological importance of the activities of the intestinal mucosa, there have been few successful attempts to study it in isolation, and the impression has arisen that it is difficult or impossible to set up a satisfactory surviving intestine preparation apart from the body and still with a viable mucosa. The objects of this paper are to show that this is not so, to describe a preparation which can be set up with uniform success, and to describe its major properties.In outline, the preparation to be described is made by cannulating at both ends a segment of small intestine in an ether-anaesthetized rat, and setting up a closed circulation through its lumen of an oxygen-saturated, C02-bicarbonatebuffered fluid before the circulation through the intestinal wall is interrupted. The segment is suspended in a bath of oxygenated Ringer, and absorptive processes are followed by sampling the fluid circulating through the lumen (inner fluid) and the fluid bathing the exterior of the intestine (outer fluid).The success of the technique is believed to depend on the feature that there is no time at which the mucosal cells are deprived of an adequate supply of oxygen. METHODSAnimal. Male albino rats of Wistar stock weighing 200-300 g. are used. The animals are taken off the stock diet 24 hr. before use, and are provided with plain water and 5 % glucose in water. They usually take about 100 ml. of the glucose-water, so that their calorie intake is reasonably maintained, but at the same time the small intestine is rendered largely free of solid contents.Anaesthesia. Induction is effected by placing the animal in a small box containing a cotton-wool pad on which ether has been poured. Light anaesthesia is maintained with an Oxford Vaporizer adapted for use with small animals.Preparation of segment8. Two segments from each animal are usually set up, the whole of the small intestine except the duodenum being used. The duodenum has been excluded in the work so far carried out because of difficulties in mobilizing it, and for fear of harmful traction on the blood vessels or the intestine.The abdomen is opened in the midline, the duodenal-jejunal flexure identified, and the intestine divided at this point. A cannula directed caudad is tied into the jejunum, the length of upper

This paper describes further work on the absorption of glucose from the surviving preparation of rat small intestine which we have previously described (Fisher & Parsons, 1949, 1950a. It was tacitly assumed in the earlier work that as the mucosa, the most active tissue of the intestinal wall, was directly in contact with the fluid in the lumen, it would draw its nourishment from this fluid. Consequently, it was supposed that disappearance of glucose from the fluid in the lumen was due to two processes: translocation of glucose into the submucosal space by some of the cells, and utilization of glucose for metabolic purposes by all of the cells. The work to be described suggests that this is not so. The intestine behaves as though glucose were translocated across the mucosa by relatively few cells, and as though the lumenal borders of the remaining mucosal cells were impermeable to glucose. The glucose concentration in the fluid in the submucosal space of the surviving intestine rises sharply during glucose absorption, and most of the glucose supply of the mucosa is presumably derived from this source.The general relation existing between glucose concentration in the lumen and the rate of absorption is described and discussed. METHODS(Glucose concentrations are expressed as percentages; the meaning here is g of glucose/100 ml.)The isolated intestine preparation of Fisher & Parsons (1949) was used. The technique of sampling circulating fluids was modified. Towards the end of the period of observation most of the circulgtiny fluid wis drainal into a voluamtric fhsk without interruption of the circulation.At the end of the period, approximately 50 ml. of glucose-free, warm, oxygenated Ringer were introduced, allowed to circulate briefly, and withdrawn as far as po33ible. The circulation was not interrupted. A further 50 ml. of Ringer were introduced and again as much fluid as possible

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Wells (1931) showed that the rate of absorption of water from the small intestine of the dog was dependent on the distension pressure. This observation has formed the basis of a view that water absorption is determined by hydrostatic and osmotic factors. The ability of the intestine to absorb the animal's own serum or an isotonic salt solution requires on this view that the absorption of water should be secondary to the absorption of the protein and salts.The surviving small intestine preparation of Fisher & Parsons (1949) provides means of obtaining further evidence of the nature of water absorption, since osmotic conditions on the two sides of the mucosa can be varied at will, -and a useful range of distension pressures can be employed. This paper describes the effects of alteration of distension pressure, osmotic pressure and other factors on the absorption of water and of urea, creatine and sorbitol.In the original work of Wells, in which very low distension pressures were used, some part, if not all, of the effect of distension might be expected to arise from the separation of mucosal folds with increasing pressure: mucosal epithelium occluded by folding cannot participate in absorptive activity. In the present work, therefore, the lowest distension pressure used has been one known, from microscopic examination of preparations fixed during distension, to separate all mucosal folds.