SUMMARY1. The rate of metabolism of glucose to lactate has been measured in a number of non-vascularly perfused preparations of rat jejunum in vitro. The glucose and lactate metabolism was measured simultaneously and under conditions such that the uptake of glucose and the appearance of lactate were linearly related to time.2. It is found that there is no difference between the rates at which rings of rat jejunum utilize glucose during the first 45 min of anaerobic or aerobic incubation. During the first 15 min of incubation between 60-70 % of the metabolized glucose was converted to lactate under aerobic conditions; this value increased to 80-90 % during the subsequent 30 min.During the period 0-15 min of incubation, lactate production was found to be higher under anaerobic than under aerobic conditions but after this initial period the rate of lactate production was the same under aerobic and anaerobic conditions.3. For segments of rat jejunum, maintained in vitro by the recirculation of nutrient fluid through the intestinal lumen, neither the rate of production of lactate, nor the utilization of glucose, was stimulated if the preparation was maintained under anaerobic rather than aerobic conditions. The direct delivery of gas into the intestinal lumen in the form of a stream of bubbles (segmented circulation) reduced both the utilization of glucose and the production of lactate under aerobic conditions. However, no effect on glucose metabolism was observed under anaerobic conditions. The finding of a Pasteur effect with the segmented-circulated preparation, but not with the simple recirculated preparation, is associated with the lower rate of aerobic lactate production in the former preparation. Reasons are given for supposing that under conditions of segmented circulation, the luminal compartment is better stirred, thereby increasing access of 02 to the tissue. P. J. HANSON AND D. S. PARSONS 4. A preparation of rat small intestine perfused through the vascular bed is described. With this preparation the rate of glucose utilization is significantly lower than that for recirculated preparations and the rate of lactate production is substantially less than that of the other preparations studied.5. With the preparation perfused through the vascular bed, and with glucose, 10 mm, present only in the vascular medium the addition of erythrocytes to the vascular infusate causes a significant reduction in both glucose utilization and in the rate of lactate production. The addition of erythrocytes to produce an haematocrit of 40 % (v/v) causes a greater reduction in glucose utilization and lactate production than is found for an haematrocrit of 15 %. About 10% of the lactate produced appears in the luminal contents. With an haematocrit of 15 %, the 02 consumption of the whole wall of the jejunum was found to be 6-4 ,mole 02 g dry wt.-' min-', equivalent to a value for the Qo. of 8 6 #d. 02 mg dry wt.-' hr-1.

1. During the absorption of isotonic solutions containing 160 mM Na, 135 mM Cl and 25 mM HCO3, the contents of rat jejunum become progressively more acid than the contents of the ileum or colon. 2. During absorption there is a net entry of total CO2 into the contents of the ileum and colon, while from the jejunum there is a net absorption of total CO2. 3. The carbonic anhydrase inhibitor 6063 depresses the absorption of water and electrolytes from the jejunum, ileum and colon, and reverses the direction of net movement of CO2 in ileal segments. 4. After absorption of saline solutions, the water content of the wall of the jejunum and colon is increased.

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

1. The metabolism and transport of glutamine and glucose were investigated in a preparation of rat small intestine perfused through the vascular bed in vitro and in situ. 2. With glucose (7.5mm) or glutamine (4.5mm) in the lumen, approx. 40% of the substrate taken up appears unchanged on the vascular side. When glutamine (1.5mm) is also added to the vascular perfusate, metabolism of glutamine is increased and there is uptake of glutamine from both the vascular bed and lumen. Orientation of substrate (vascular bed or lumen) influences the value of alanine production/glutamine utilization and lactate production/glucose utilization. 3. Deprivation of food and metabolic acidosis have no effect upon the utilization of glutamine by unit length of jejunum. In fed rats, glutamine utilization is 44% of glucose utilization, but in rats deprived of food it is 112% of glucose utilization. 4. Glucose utilization and lactate production are not significantly altered by the presence of glutamine in the vascular bed or lumen. 5. With glucose only in the vascular perfusate, glucose utilization is the same in jejunum and ileum. Glutamine metabolism in the ileum is 28% lower than in the jejunum. 6. Glutamine utilization is dependent on the concentration of glutamine in the vascular perfusate, but is not significantly affected by the absence of glucose. 7. Results are discussed in relation to the role of intestinal glutamine metabolism and with respect to some problems of the transepithelial movement of substrates that are both transported and metabolized.