The utilization of glucose and production of lactate by in vitro preparations of rat small intestine: effects of vascular perfusion.

Abstract

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.

Ascorbic Acid in Intestinal Tissues

“…The substitution for the in vivo blood supply by an oxygenated incubation medium makes the size ofthe tissue portions of paramount importance. In investigation of intestinal function, mucosai strips, rings oi' intestine, everted sacs and even the use of vascular perfusion have been tried (Hanson and Parsons, 1976). Differences of opinion exist on the viability of these preparations, but it is considered that the use of Krebs-saline with at least 95% oxygen and experimentation up to 60 min is satisfactory ( Levin and Syme.…”

“…Differences of opinion exist on the viability of these preparations, but it is considered that the use of Krebs-saline with at least 95% oxygen and experimentation up to 60 min is satisfactory ( Levin and Syme. 1975: Bronk, Leese and Parsons, 1976: Hanson and Parsons, 1976. In order to provide as small a difTusion distance as possible, thin rings of intestine were compared with intestinal strips for ability to retain their ascorbate content.…”

The vascularly and luminally perfused small intestine in vitro: dissection technique and model system

“…In our experience, human erythrocytes with subnormal ATP concentrations 'plugged' the intestinal microvasculature; the perfusion then invariably failed [the diameters of human, rat and bovine red cells are about 7' 5, 7, 0 and 6/tm, respectively (Weinstein, 1974;Altman & Dittmer, 1974); erythrocytes from anyone of these sources must deform (Mar~el, 1979)if they are to pass through precapillary sphincters in rat intestinal villi with an internal diameter of 4/tm (Bohlen et al, 1975)]. Decreasing the haematrocrit may avoid some of this plugging of microcapillaries but is 181 not sound practice; it does not solve the basic problem and necessarily diminishes the amount of O 2 delivered to the tissue (Hanson & Parsons, 1976). A normal erythrocyte Gri-2,3-P 2 concentration is required if 02-loaded erythrocytes are to unload their O 2 in response to tissue respiration demands (this requirement does not apply to bovine red cells).…”

“…Leave one end of this ligature long and free to aid later exposure of the portal vein. Resection of the duodenum (Hanson & Parsons, 1976) is unnecessary; it is best left in situ so as to avoid any possibility of haemorr hage. Now retract the jejunum using the excess jejunal ligature threads mentioned above, make a O· 5 cm incision with fine-pointed iris scissors along the relatively avascular antimesenteric border distal to these threads and insert the proximal luminal cannula; tie it in with the distal ligature thread previously left loose round the jejunum.…”

“…Descriptions exist of the results obtained with the perfused intestine in experimental practice in vivo and in vitro (e.g. Windmueller et al, 1970;Ross, 1972;Hanson & Parsons, 1976Windmueller & Spaeth, 1980;Nicholls et al, 1983;Holloway & Parsons, 1984;KeIlet et al, 1984), but descriptions of the dissections involved are sparse and lack many essential details; little attention has been given to the preparation and properties of erythrocytes for inclusion in the vascular perfusion medium.…”