Functional, biochemical and morphological alterations in the intestines of rats with an experimental blind-loop syndrome

Tight junction regulation during impaired ion transport in blind loops of rat jejunum

Epithelial cell tight junction structure in self-filling blind loops of rat jejunum, a model for blind loop syndrome in humans, was analyzed morphometrically along the crypt-villus axis. In control jejunum, the number of strands and junctional depth, including meshwork depth, decreased from crypt to villus tip. In the blind loop, aberrant strands appeared below the meshwork, particularly in crypt cells. Consequently, total junctional depth was greater than in controls. Furthermore, strand number and junctional meshwork depth were increased in blind loops at the villus tip. It is that site along the crypt-villus axis which showed the most shallow junction in control jejunum. This structural change is paralleled by a three-fold increase in epithelial resistance as previously measured by alternating current impedance analysis. Relative Na over Cl permeability (PNa:Cl) was obtained from dilution potential measurements. PNa:Cl was 1.50:1 in control jejunum and 1.35:1 in the blind loop (n.s.). Considering the cation selectivity of the tight junction, the increase in epithelial resistance in blind loops cannot be attributed to a collapse of the lateral intercellular space but is due to changes in tight junctional permeability resulting from structural alteration. The blind loop syndrome represents a further example of diminished epithelial ion transport and concomitant decrease in tight junction permeability, thus supporting the general concept of regulation of the tight junction in response to active transport activity.

Response of the jejunal mucosa of dogs with aerobic and anaerobic bacterial overgrowth to antibiotic therapy

Dogs with naturally occurring aerobic or anaerobic bacterial overgrowth have been examined before and after antibiotic therapy in order to assess reversibility of damage to the jejunal mucosa. Histological changes in peroral jejunal biopsies were relatively minor before and after treatment, but sucrose density gradient centrifugation revealed specific biochemical abnormalities that responded to antibiotic therapy. Aerobic overgrowth was initially associated with a marked loss of the main brush border component of alkaline phosphatase activity; this recovered following treatment, suggesting that aerobic bacteria may cause reversible damage to the hydrophobic region of the brush border membrane. In contrast, anaerobic overgrowth was initially associated with a marked reduction in brush border density, indicative of a considerable fall in the glycoprotein-to-lipid ratio of the membrane. Density increased from 1.17 to 1.21 g/ml after antibiotic therapy, consistent with recovery from this relatively severe damage to the brush border caused by anaerobic bacteria. Reductions in soluble and peroxisomal catalase activities which could compromise mucosal protection against free radicals in dogs with aerobic overgrowth, and a loss of particulate malate dehydrogenase activity indicative of mitochondrial disruption in dogs with anaerobic overgrowth, were also reversed after treatment. These findings indicate that aerobic and anaerobic bacterial overgrowth can result in contrasting but potentially reversible damage to the jejunal mucosa which would not be detected by conventional investigative procedures.

Comparison of the biochemical changes in the jejunal mucosa of dogs with aerobic and anaerobic bacterial overgrowth

Subcellular biochemical changes in the jejunal mucosa have been compared in dogs with either aerobic or anaerobic bacterial overgrowth to explore relationships between composition of the flora and mucosal damage. Affected animals comprised 17 German shepherd dogs with chronic diarrhea or weight loss, or both. Analysis of duodenal juice demonstrated aerobic overgrowth in 10 cases, most frequently comprising enterococci and Escherichia coli, and obligate anaerobic overgrowth in 7 cases, most frequently including Clostridia spp. Histologic changes were minimal; however, examination of peroral jejunal biopsy specimens by sucrose density gradient centrifugation revealed specific biochemical abnormalities. In the dogs with aerobic overgrowth, there was a selective loss of brush border alkaline phosphatase activity, and gamma-glutamyl transferase activity was increased, whereas activities of disaccharidases and aminopeptidase N were unaltered. In contrast, anaerobic overgrowth was associated with a reduction in brush border density, indicative of a considerable fall in the glycoprotein-to-lipid ratio of the brush border membrane, whereas brush border enzyme activities were unaltered. There was a loss of peroxisomal catalase activity in dogs with aerobic overgrowth, and an indication of mitochondrial disruption in dogs with anaerobic overgrowth, but little evidence for damage to other subcellular organelles. These findings demonstrate that aerobic and anaerobic overgrowth may be associated with distinct but different mucosal abnormalities particularly affecting the brush border membrane.

Impaired intestinal sodium and chloride transport in the blind loop syndrome of the rat

Self-filling blind loops of rat jejunum were used as a model for the blind loop syndrome in humans. Electrical resistance, short circuit current, and unidirectional sodium and chloride fluxes were measured using the Ussing technique. Whereas net fluxes for sodium and chloride did not differ significantly from zero in the blind loop or in the control, unidirectional fluxes of either direction were decreased and electrical resistance was increased, indicating an increase in the tightness of the intestinal wall. Measurements of alternating current impedance and micropuncture experiments revealed that this was due to an increase in epithelial resistance from 9 +/- 1 omega X cm2 (n = 15, results of both methods) to 27 +/- 4 omega X cm2 (n = 15) and in subepithelial resistance from 40 +/- 2 omega X cm2 (n = 15) to 76 +/- 7 omega X cm2 (n = 15). As the ratio of epithelial to subepithelial resistance was similar in the blind loop and in the control, lower transport rates in the blind loop are indicative of impaired epithelial transport function. Subsequently, two different transport systems were characterized. First, the 3-o-methyl-glucose-induced, phlorizin-reversible increase in short circuit current, representing glucose-coupled sodium absorption, showed a 77% decrease in maximum velocity in the blind loop and no change in Km. Second, the chloride-induced, bumetanide-reversible increase in short circuit current in tissues stimulated simultaneously by prostaglandin E1 and theophylline, representing rheogenic chloride secretion, also showed a decrease in maximum velocity (of 83%) and no change in Km. A morphometric analysis revealed that the crypt surface area increased by 100% in the blind loop, whereas the villous surface area was not significantly different between blind loops and controls. We conclude that the jejunal self-filling blind loop is characterized by impaired active ion transport processes and an increase in epithelial and subepithelial resistance.

Adaptation of the jejunal mucosa in the experimental blind loop syndrome: changes in paracellular conductance and tight junction structure

Self-filling blind loops of rat jejunum exhibit hyperregenerative transformation of the mucosa. We used this experimental model to characterise mechanisms, which may occur under similar conditions in man (stagnant loop syndrome). Epithelial and subepithelial resistance were measured in the Ussing-chamber by voltage divider ratio measurements after positioning a microelectrode between epithelium and subepithelial tissue layers. In the blind loop, epithelial resistance increased from 8 +/- 1 to 23 +/- 1 omega cm2 and subepithelial resistance from 39 +/- 4 to 86 +/- 8 omega cm2 as compared with control jejunum. The increase in the subepithelial resistance was paralleled anatomically by an increase in the thickness of the subepithelial tissue layers from 63 +/- 4 microns to 177 +/- 19 microns. Ultrastructural analysis of the tight junction area by freeze fracture electron microscopy revealed an increase in the total junctional 'depth' in the crypts from 243 +/- 9 nm in control jejunum to 396 +/- 17 nm in the blind loop, while the number of horizontally oriented 'strands' remained unchanged. Villus tight junctions did not differ between blind loop and control. We interpret the alterations in the self-filling blind loop as an adaptive response of the epithelium which reduces backleakage of already absorbed electrolytes across the tight junction into the intestinal lumen. This mechanism is suitable to support the intestine in maintaining body electrolyte and water contents during cellular electrolyte malabsorption.

Pathogenesis of the mucosal hyperplasia in self-filling blind loops of rat jejunum: a morphometric study in germ free animals

Bacterial overgrowth and high intraluminal concentrations of deconjugated bile acids are thought to be responsible for mucosal hyperplasia in self-filling blind loops of rat jejunum. To investigate this hypothesis further we have assessed the three dimensional architecture of these loops created in germ free animals without or with di- or mono-association of different bacterial species. It was found that mucosal hyperplasia develops in the absence of any bacterial contamination and that bacterial association does not lead to a more pronounced mucosal proliferation. This implies that other mechanisms provoke this morphological phenomenon. Increased bulk contents in these loops or immunological events are probably the most likely explanation.

Review: pathophysiology of diarrhea caused by bacterial overgrowth of the small intestine

The bacterial overgrowth syndrome constitutes an intestinal problem involving alterations in motility and injury to the brush border and mucosa. The overgrowth of bacteria also causes secretion, malabsorption, and maldigestion. These alterations result in a clinical syndrome that manifests itself as weight loss, malabsorption of specific nutrients, and (usually) diarrhea. There are known causes of bacterial overgrowth, such as intestinal diverticuli or surgical procedures involving a vagotomy, but in our experience most cases remain idiopathic. This review evaluates the mechanisms of bacterial overgrowth, as currently understood, and specifically addresses the known causes of diarrhea that results from bacterial contamination of the small intestine.

Biochemical changes in the jejunal mucosa of dogs with a naturally occurring enteropathy associated with bacterial overgrowth

The subcellular biochemical features of a naturally occurring enteropathy in the dog associated with bacterial overgrowth have been examined. Affected animals comprised a group of 10 German Shepherd dogs with raised serum folate and reduced vitamin B12 concentrations, mild steatorrhoea, reduced xylose absorption, and normal exocrine pancreatic function. Culture of duodenal juice showed bacterial overgrowth with mixed flora, most frequently including enterococci and Escherichia coli. Examination of peroral jejunal biopsies revealed predominantly minimal histological but distinct biochemical abnormalities in the mucosa. The specific activity of alkaline phosphatase was decreased, isopycnic density gradient centrifugation showing a marked loss particularly of the brush border component of enzyme activity. In contrast, gamma-glutamyl transferase activity was enhanced in brush border fragments of slightly increased modal density, but there were no changes in the activities of the carbohydrases, zinc-resistant alpha-glucosidase, maltase, sucrase, and lactase or of the peptidase, leucyl-2-naphthylamidase. Activities of lysosomal enzymes were increased and there was evidence for enhanced lysosomal fragility and mitochondrial disruption. The activities and density gradient distributions of marker enzymes for basal-lateral membranes, endoplasmic reticulum and peroxisomes were essentially unaltered. These findings show that bacterial colonisation of the proximal small intestine may be associated with specific alterations in microvillus membrane proteins and provide biochemical evidence for intracellular damage to the enterocytes.

[Structural and functional findings in experimental blind loop syndrome]

Proximal and distal the blindsack a villus and crypt prolongation connected with a decreasing absorption of octanoate could be pointed out. The structural changes are very likely a hyperplasia of the mucosa. Within the blindsack a hyperplasia in connection with an accelerated proliferation of cells and an almost three and a halffold enlargement of the surface of the villi could be found. Simultaneously, the mucosa was damaged. An artificial bile duct as well as a neomycin therapy caused a decrease of the structural and functional changes but did not prevent the mucosal hyperplasia. These results are explained with adaptive processes of the small intestinal mucosa in a sense of hyperregeneration alterations of sprue typus.

Enzymatic activities in jejunal biopsy specimens from patients with the stagnant-loop syndrome

The activity of the marker enzymes lactase, sucrase, neutral alpha-glucosidase, alkaline phosphatase, gamma-glutamyl transferase, leucyl-beta-naphthylamidase (brush border); 5-nucleotidase (basolateral membrane); and acid phosphatase and N-acetyl-beta-glucosaminidase (lysosomes) in jejunal biopsies from patients with the stagnant-loop syndrome and controls was studied. The activity of gamma-glutamyl transferase was increased in the patient group; the activity of the other enzymes did not differ significantly in patients and controls. The DNA to protein ratio was increased in the patient group. The results do not support the hypothesis of epithelial damage in the human stagnant-loop syndrome.

Dysfunction of the continent ileostomy: clinical features and bacteriology

The pathogenesis and treatment of dysfunction of the continent ileostomy was investigated in 12 patients, five of whom had asymptomatic malabsorption and seven of whom had acute complaints. The number of anaerobic bacteria in jejunal aspirates was increased in patients with pouch malfunction (range 10(3) to 10(8)/g aspirate), but the microbiology of ileal effluent and the morphology of the ileal mucosa could not be correlated with dysfunction. Bile acid breath tests and lactose tolerance tests were not, however, reliable indicators of jejunal bacterial overgrowth. The symptoms, the malabsorption, and the number of jejunal and ileal anaerobic bacteria decreased in patients during treatment with metronidazole, implicating overgrowth of anaerobic bacterial flora in the pathogenesis of the syndrome.

Adaptative response of alpha- and beta-glucosidase kinetics along the villi of rat self-filling jejunal blind loops

Four and 12 days after the construction of self-filling jejunal blind loops in the rat, the apparent Km- and Vmax-values of lactase/beta-glucosidase and neutral alpha-glucosidase were determined by in-situ quantitative enzyme histochemistry, and changes in the villus-crypt architecture of the mucosa were examined by microdissection. The results were compared with corresponding data from sham-operated controls. The kinetics data were obtained from the base and the transition zone between medium and apical villus third by the use of a microdensitometric technique. The apparent Vmax of lactase/beta-glucosidase is significantly smaller than in the control rats at both measuring sites of the villi and even decreases from day 4 to day 12. The apparent Vmax of neural alpha-glucosidase is not affected, and thus the same increase in enzyme activity along the villi as in the controls is observed. The apparent Km of this enzyme, however, is already significantly increased on day 4 at both villus positions in the blind loops. A pronounced increase in villus surface area is detected in the blind loops as a result of an increase in crypt cell proliferation. The results indicate that enzymatic adaptation in the self-filling blind loops of rat jejunum exhibits different patterns for brush border alpha- and beta-glucosidases and is at least in part accomplished independently of the pronounced mucosal transformation occurring in this experimental condition.

Effect of secreted Bacteroides proteases on human intestinal brush border hydrolases

Selected bacteroides species secreted various amounts of protease and glycosidase into their growth medium. Bacteroides vulgatus, distasonis, and ovatus secreted the most (31-60% of total). The secreted protease was similar in action to the protease within the organism, in that it had a broad pH optimum of 6-9, a K(m app.) for casein of 0.1 muM, and was inhibited by benzamidine, phenylmethylsulfonyl fluoride, diisopropylfluorophosphate (DIFP), and by an elastase inhibitor, Ac(Ala)(3)AlaCH(2)Cl. Exposure of human brush border preparations to the secreted protease reduced maltase and sucrase activities; the reduction could be prevented by DIFP. In contrast, brush border alkaline phosphatase activity either did not change or increased after exposure to bacterial secretions. >90% inhibition of secreted glycosidase using EDTA and p-chloromercuribenzoic acid did not prevent the reduction of brush border maltase and sucrase activity, suggesting that glucosidases were not likely to be involved in the destruction of brush border enzymes. Moreover, the bacterial proteases caused only a small net release of active maltase or sucrase from the brush border. Most of the loss of activity was due to destruction of the enzyme. Proximal bowel fluid of three patients with overgrowth contained DIFP-inhibitable protease that destroyed sucrase in isolated brush borders. A Bacteroides species was isolated from each sample that secreted protease and destroyed brush border sucrase. We conclude that in bacterial overgrowth syndromes, brush border damage may occur from protease(s) secreted by Bacteroides.

[The effect of unconjugated bile salts on the intestinal absorption of electrolytes and water in the proximal jejunum. Studies in conscious rats (author's transl)]

With an in vivo-perfusion-technique the influence of unconjugated bile salts (cholate, desoxycholate) on the net electrolyte and volume absorption is studied in the jejunum of conscious rats. The applied doses correspond to physiological concentrations in the intestine of rats. Control experiments were performed in the same animal. Cholate and desoxycholate diminish the net electrolyte and volume absorption resp. cause a net secretion. The effects are largely reversible. The extent of net volume absorption depends on the applied dose of each bile salt. The possible mode of action of unconjugated bile salts on the electrolyte and water absorption in the small intestine is discussed.

Acute distal intestinal obstruction in gnotobiotic rats. Intestinal morphology and cell renewal

1. Complete mechanical obstruction of the distal small intestine was produced in gnotobiotic rats. 72 h after the operation small intestinal morphology and epithelial cell renewal were investigated proximal and distal to the site of obstruction. 2. Proximal to the site of obstruction there were minor changes in villus height, base length and in villus cell number, a large increase in depth and diameter of the crypts and an approximately threefold increase in cell renewal. 3. Distal to the site of obstruction there were no differences between the intestines of rats with obstruction and controls. 4. The apparent lack of secretion by the goblet cells and the reduced number of intraepithelial leucocytes suggest that the barrier function of the small intestine is impaired in obstruction.