Villus Damage Research Articles

Primary sensory nerves mediate in part the protective mesenteric hyperemia after intraduodenal acidification in rats

Background: The mechanism of intraduodenal HCl-induced mesenteric hyperemia is unknown. In anesthetized rats, the hypothesis that the primary sensory nerves mediate the intraduodenal HCl-induced protective mesenteric hyperemia was tested. Methods: The hyperemic response in the superior mesenteric artery (SMA) and superficial villus damage after intraduodenal bolus administration of saline, 0.03N, or 0.1N HCl were measured. These changes induced by 0.1N HCl after mucosal anesthesia (1% lidocaine) or afferent nerve ablation (125 mg/kg subcutaneous capsaicin) were evaluated. The duodenal villus damage induced by intraduodenal perfusion of 0.1 N HCI after mucosal afferent nerve stimulation by intraduodenal capsaicin or afferent nerve ablation by subcutaneous capsaicin was examined. Results: Intraduodenal bolus administration of HCI produced a dose-related increase in SMA blood flow and villus tip damage. The mesenteric hyperemia induced by 0. 1N HCI was significantly reduced, but the villus tip damage was not altered by prior intraduodenal lidocaine or subcutaneous capsaicin. The deep duodenal villus damage produced by intraduodenal perfusion of 0. 1N HCl was decreased by intraduodenal but increased by subcutaneous capsaicin. Conclusions: The capsaicin-sensitive afferent nerves mediate in part the HCl-induced mesenteric hyperemia. They protect against the deep but not the superficial duodenal villus damage induced by HCI.

Role of T lymphocytes in intestinal mucosal injury

To determine the role of T cells versus mast cells in mucosal injury, we documented structural and functional changes in the intestine of congenitally athymic nude rats during infection with the enteric parasite, Nippostrongylus brasiliensis. Studies were conducted at days 4, 7, 10, and 21 postinfection; controls were uninfected. Villus damage was indicated by morphological abnormalities at days 7, 10, and 21 and reduced activities of disaccharidase enzymes at days 10 and 21. The activity of the proliferative enzyme, thymidine kinase, was increased only at day 21, at which time the crypts were elongated. Epithelial permeability increased significantly: 5-hr recovery (in urine and blood) of the probe molecule, [51Cr]EDTA, following injection into ligated jejunal segments, was elevated at days 7 and 10. Uptake of a protein antigen, ovalbumin, from lumen to blood followed a similar pattern. No evidence of functional T cells was demonstrated. However, mucosal mast-cell activation was indicated by elevated serum levels of rat mast-cell protease II at days 7 and 10. We conclude that the absence of thymus-derived T cells does not preclude mucosal damage involving impaired barrier and digestive function. Mucosal mast cells may be involved in causing the injury in this model.

Direct Evidence for the Involvement of Free Radicals in Ischemic Insult to the Intestine

Ischemia of rat intestine was induced in vivo by occlusion of the superior mesenteric artery (SMA) for 15 min. Sodium salicylate, 100 mg/kg, given IP, 30 min prior to the ischemic event served as a specific trap for hydroxyl radicals and provided direct evidence for the involvement of free radicals during the ischemic insult. Portions of the bowel were sequentially isolated and removed. The hydroxylation products, dihydroxybenzoic acid (DHBA) derivatives were isolated, identified and quantified by HPLC coupled with electrochemical detection (ECD). The level of 2,5-DHBA (Mean +/- SE, ng/g tissue) in the preischemic bowel (N = 21) was 241.8 +/- 10.0. It rose significantly to 313.3 +/- 15.5 in the ischemic specimen (p = 0.0129) and remained unchanged in the reperfusion period (322.8 +/- 15.5). The histological examination correlated well with these levels: mild villi damage in the ischemic period with no further damage in the reperfusion period.

Antigen-Induced Mucosal Damage and Restitution in the Small Intestine of the Immunized Rat

Intestinal mucosal damage and restitution were examined following antigen-induced systemic anaphylaxis in Nippostrongylus brasiliensis immunized rats. The rats were injected intravenously with N. brasiliensis antigen or saline. At 60 min, morphological and biochemical parameters were determined in jejunum and ileum, and the epithelial permeability was assessed by measuring recovery of 51Cr-ethylenediaminetetraacetic acid in the blood after injecting it into a ligated segment. Antigen challenge resulted in significant abnormalities: (1) villus damage with sloughing of enterocytes; (2) decreased activities of brush border enzymes; (3) decreased levels of mucosal histamine and rat mast cell protease II (mast cell mediators), and (4) increased uptake of 51Cr-ethylenediaminetetraacetic acid. Progression of the injury was examined by taking consecutive biopsies at 15-min intervals for 60 min and then at 5 h. At 15 min, an abnormality was present in all sections which ranged from minor oedema and enterocyte detachment at villus tips to virtual complete destruction of the apical region. Restitution occurred by villus contraction with migration of the epithelium over the damaged regions. At 5 h, the epithelium had resealed, but the villi were significantly reduced in height.

An Electron Microscopic Investigation of Time‐Related Changes in the Intestine of Neonatal Mice Infected with Murine Rotavirus

SummarySeven‐day‐old mice were infected orally with murine rotavirus (EDIM) and regions of the gut examined at 24 h intervals up to 7 days by electron microscopy. Structural changes were correlated with data on viral antigen production, thymidine kinase activity, and clinical signs of diarrhea. No pathological changes were detected in the colon. Infection and structural damage were confined to the small intestine, with middle regions showing the most pronounced changes. Constriction of villus bases, edema of the lamina propria, and vacuolation of enterocytes occurred at 24 h postinfection (PI), i.e., before evidence of major virus replication. Transient villus atrophy occurred at 48 h PI. Recovery of villus length was evident by 72 h PI accompanied by evidence of marked enterocyte replication at villus bases. Many enterocytes were damaged with little evidence for the presence of virus particles. By 96 h PI, villi had almost recovered from infection although some enterocytes were still damaged; no virus particles were detected in these cells. A second phase of villus damage and edema of the lamina propria occurred at 120 h PI; the pathology resembled that at 24–48 h PI. By 144 to 168 h PI, recovery of the mucosa from infection was virtually complete. We suggest that many of the pathological features following rotavirus infection result from rotavirus‐induced ischemia of villi and that diarrhea results from malabsorption of fluid by damaged villi and hypersecretion of ions released from increased numbers of dividing cells at villus‐crypt borders.

An electron microscopic investigation of time-related changes in the intestine of neonatal mice infected with murine rotavirus.

Seven-day-old mice were infected orally with murine rotavirus (EDIM) and regions of the gut examined at 24 h intervals up to 7 days by electron microscopy. Structural changes were correlated with data on viral antigen production, thymidine kinase activity, and clinical signs of diarrhea. No pathological changes were detected in the colon. Infection and structural damage were confined to the small intestine, with middle regions showing the most pronounced changes. Constriction of villus bases, edema of the lamina propria, and vacuolation of enterocytes occurred at 24 h postinfection (PI), i.e., before evidence of major virus replication. Transient villus atrophy occurred at 48 h PI. Recovery of villus length was evident by 72 h PI accompanied by evidence of marked enterocyte replication at villus bases. Many enterocytes were damaged with little evidence for the presence of virus particles. By 96 h PI, villi had almost recovered from infection although some enterocytes were still damaged; no virus particles were detected in these cells. A second phase of villus damage and edema of the lamina propria occurred at 120 h PI; the pathology resembled that at 24-48 h PI. By 144 to 168 h PI, recovery of the mucosa from infection was virtually complete. We suggest that many of the pathological features following rotavirus infection result from rotavirus-induced ischemia of villi and that diarrhea results from malabsorption of fluid by damaged villi and hypersecretion of ions released from increased numbers of dividing cells at villus-crypt borders.

Effect of Extracellular Calcium Depletion on Epithelial Structure and Function in Rabbit Ileum: A Model for Selective Crypt or Villus Epithelial Cell Damage and Suggestion of Secretion by Villus Epithelial Cells

The epithelium of mammalian small intestine can be conveniently divided into two compartments: the crypt and the villus. These compartments are not only structurally distinct but also may be functionally distinct with regard to sodium and chloride ion transport. Villus epithelial cells are thought to be responsible for electrolyte absorption and crypt cells for secretion of ions and water. We show that exposure of rabbit ilea] mucosal sheets in vitro to bathing solutions depleted of calcium with 1 mM ethyleneglycol-bis (β-aminoethylether)-N,N'-tetraacetic acid on either the mucosal or the serosal surface produces selective damage of one epithelial compartment while leaving the other structurally intact. Thus these preparations represent a potential in vitro model for studying the relative contribution of crypt and villus epithelium to net transepithelial active ion transport. The effects of selective mucosal or serosal extracellular calcium depletion on epithelial structure were studied in detail using light and electron microscopy and freeze-fracture techniques. The functional significance of the structural abnormalities produced in these models was evaluated by measuring unidirectional sodium and chloride ion fluxes and serosal theophylline-dependent and mucosal glucose-dependent increases in short-circuit current. Serosal depletion of extracellular calcium produced diffuse damage to crypt epithelial cells, which consisted of vacuolization, detachment from the basement membrane, and dissolution of tight junctions, but which produced no detectable structural damage to villus epithelial cells. These structural alterations produced a decrease in basal shortcircuit current, an increase in transepithelial conductance and in net sodium and chloride ion absorption, no effect on the glucose-induced increase in short-circuit current and a significant decrease in the theophylline-induced short-circuit current response. In contrast, mucosal depletion of extracellular calcium resulted in vacuolization of a large portion of villus epithelial cells with concomitant detachment from the basement membrane and tight junction dissolution, but produced no structural defect in crypt epithelial cells. These alterations were associated with an increase in transepithelial conductance, no significant change in basal net sodium and chloride ion transport, and significant decreases in both glucose and theophylline-induced short-circuit current response. Furthermore, the decrease in theophylline-induced short-circuit current responses seen in tissues with selective villus damage but structurally intact crypts was at least as great as that seen with selective crypt damage. These data support the concept that crypt epithelium actively secretes and villus epithelium actively absorbs sodium and chloride ions. In addition, however, they suggest that a population of epithelial cells on the intestinal villi may also have the capacity to secrete electrolytes.

Intraepithelial Lymphocyte Count and Crypt Hyperplasia Measure the Mucosal Component of the Graft-versus-Host Reaction in Mouse Small Intestine

We have used measurements of intestinal epithelial cell kinetics and counts of intraepithelial lymphocytes and mucosal mast cells to measure small intestinal mucosal changes during the proliferative and recovery phases of graft-vs.-host reaction in neonatal mice. Unirradiated (CBA x BALB/c)F1 mice were injected with parental spleen cells or with culture medium at 6-8 days of age, and followed up for 9 wk thereafter. The spleen index was used as a measure of the graft-vs.-host reaction, a stathmokinetic technique with microdissection was used to measure villus and crypt lengths and crypt cell production rate, and intraepithelial lymphocytes and mucosal mast cells were counted in histologic sections. Intraepithelial lymphocyte count rose within 24 h of induction of the graft-vs.-host reaction and increases in crypt length and in crypt cell production rate occurred within 3 days. These indices exactly parallel the spleen index during the proliferative phase of the graft-vs.-host reaction and the changes occurred in the absence of any villus damage. Mucosal mast cell numbers also increased, but the rise was delayed and sustained when compared with other mucosal changes. These results show that measurements of mucosal architecture and intraepithelial lymphocyte counts can be used to quantify mucosal cell-mediated immune reactions. In addition, this study provides further evidence to support our hypothesis that the mechanism of these changes is due to a delayed-type hypersensitivity reaction in the intestinal mucosa rather than to the action of cytotoxic T lymphocytes.