The experimental infection of mice with Yersinia enterocolitica serotype 08 was investigated in a quantitative and histological study. The course of bacterial penetration and spreading was precisely determined by immunohistochemical staining. After oral administration, the bacteria passed the epithelial barrier of the ileum and spread into the lamina propria. By preference they entered Peyer's patches, which were about 1,000 times more heavily colonized than the surrounding epithelium of a comparable surface area. The bacteria proliferated in the follicles, from which they spread into the lamina propria of the vili. At either site most of the bacteria multiplied extracellularly, with only a small percentage observed to be present within the phagocytes. The bacteria did not appear to be able to pass the intact basement membrane; hence, the integrity of the basement membrane is likely to play a role in determining the route of entry and limit of spread of Y. enterocolitica infection.

In this study the early phase of the morphological adaptation of rat ileum after a proximal resection of 60% has been studied using microdissection and cell labelling techniques. Resected rats and sham-operated controls were killed 2, 4, 6, 10 and 12 days after surgery. Intraperitoneal injections of 3H-thymidine were carried out 24 or 12 h prior to sacrifice. In the latter groups mitotic arrest was achieved by vincristine. A stereo-microscope was used to measure and calculate the following parameters: intestinal diameter; villus: height, width, breadth at base and apex, surface, enterocytes per 100 micrometers length, cell pool, number of villi and absorptive surface per mm2 serosal area; crypt: length, enteroblasts per 100 micrometers length and per column, cell columns and mitoses per crypt, cell pool, crypts, and mitoses per unit serosal area; cell kinetics: migration rate, villus transit time. To test the influence of treatments, postoperative time course and the location of the intestinal segment and their possible interactions, factorial analyses of variance were carried out on the parameters investigated. The main findings, demonstrated for the first time, were: 1. An increase in the villus surface which was achieved by proportional enlargement of villus geometry; 2. This increase in the villus surface led to an enlarged absorptive surface per unit serosal area; 3. A reduction of villus transit time of the individual enterocyte; 4. A most pronounced magnitude of adaptative response in the proximal remnants which was gradually diminished in aboral direction, and 5. A sequential course of adaptative response of the various crypt parameters investigated.

SUMMARY The present study was undertaken to determine the influence of hyperphagia on the adaptive changes occurring in the rat jejunal mucosa as a result of intestinal resection. One group of resected rats was subjected to pair feeding with a sham-operated population, whilst another group was nourished ad libitum.The animals which ate ad libitum developed hypertrophy of the mucosa which was accompanied by increased glucose absorption in vivo without changes in enzyme levels. These alterations were much less pronounced in the pair-fed group of resected animals, a finding that indicates that the adaptive changes are at least partially influenced by increased luminal nutrition.Resection of a proximal or distal part of the small bowel provokes a marked hypertrophy of the mucosa of the remaining intestinal segment, which is accompanied by an increase in its absorptive capacity in vivo. Much attention has been directed to the role played by the increased intraluminal nutrition, accentuated by the onset of hyperphagia in such animals, in the development of this adaptation (Booth, Evans, Menzies, and Street, 1959;Dowling, 1974). In addition to much indirect evidence in favour of the hypothesis that luminal nutrition is essential for the maintenance of mucosal structure and function, we have recently provided a direct indication of the importance of the intestinal contents, when we demonstrated that the introduction of glucose into an excluded self-emptying blind. loop partially reversed the atrophy provoked by the process of exclusion from continuity (Menge, Werner, Lorenz-Meyer, and Riecken, 1975). The present study was undertaken to explore under pair-fed and free-fed conditions the behaviour of the intestinal mucosa following resection so that the influence of food consumption, and hence of the luminal nutrition, on the adaptive changes in the mucosa could be directly investigated. ' MethodsFemale Wistar rats weighing 170-190 g were employed. They were initially fed ad libitum with ground Altromin rat chow and tap water. OPERATIVE TECHNIQUEA resection of approximately 60 % of the distal small intestine (IR) was performed under ether anaesthesia on 14 rats, and continuity of the gut was restored by end-to-end anastomosis. A further nine rats underwent a sham operation, whereby the intestine was cut and re-anastomosed without resection. POSTOPERATIVE PROCEDURESFollowing the operation, the rats were transferred to metabolic cages which permitted an exact evaluation of the daily food consumption. For the first three days after the operation, the animals were nourished simply with a sugared salt solution. Thereafter, nine of the ileal resected animals were provided only with the quantity of solid food that the paired controls had consumed on the preceding day. The food intake and the body weight of each animal of these two groups were measured daily. The remaining five ileal resected animals received their food ad libitum. On the 32nd postoperative day the intestines were examined. LABORATORY INVESTIGATIONSDetermination...

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Summary.The functional and structural characteristics of the ileal remnant of rat intestine were examined four weeks after 45%, 70% or 95% proximal resection.The increase in villus height in the ileal remnant had already reached its maximum after a resection of 45%, whereas a further increment in the length of the crypts occurred after 70% resection. There was an increase in the number of enterocytes per unit length of villus and a rise in the DNA content per unit weight of mucosal scrapings, which testifies to the development of mucosal hyperplasia in this situation.The specific activities of sucrase, measured biochemically, and of nonspecific esterase, determined histochemically, were reduced in proportion to the extent of the resection. Similarly, the uptakes of L-phenylalanine and of fl-methyl-D-glucoside by intestinal rings in vitro were progressively diminished in the ileal remnant.There was an increase in the rate of disappearance of glucose from a perfused loop in vivo, when expressed in terms of unit intestinal length. Galactose absorption remained unchanged, but when expressed in terms of unit dry tissue, was significantly reduced, in agreement with the diminished transport of both amino-acids and monosaccharides in vitro.