The role of the mucus gel layer in intestinal bacterial translocation

Chlorpyrifos Exposure During Perinatal Period Affects Intestinal Microbiota Associated With Delay of Maturation of Digestive Tract in Rats

OBJECTIVES

Pesticide exposure via residues in food may be especially harmful when it takes place in the developing child. The present study was designed to assess the impact of perinatal exposure to chlorpyrifos (CPF, an insecticide known to cross the placental barrier).

METHODS

Female rats were exposed to oral CPF (1 or 5 mg kg day vs vehicle controls) from gestation onset up to weaning of the pups that were individually gavaged (CPF or vehicle) thereafter. Two developmental time points were studied: weaning (day 21) and adulthood (day 60). After sacrifice, samples from the intestinal tract and other organs underwent microbiological and histological analyses.

RESULTS

Rat pups exposed to 5 mg kg day CPF were both significantly smaller (body length) and lighter than controls. Exposure to CPF was associated with changes in the histological structures (shorter and thinner intestinal villosities), an intestinal microbial dysbiosis, and increased bacterial translocation in the spleen and liver. These significant microbial changes in the gut were associated with impaired epithelium protection (mucin-2) and microbial pattern recognition receptor (Toll-like 2 and 4) gene expression.

CONCLUSIONS

Exposure to CPF during gestation and development affected the pups' intestinal development, with morphological alteration of the structures involved in nutrient absorption, intestinal microbial dysbiosis, alteration of mucosal barrier (mucin-2), stimulation of the innate immune system, and increased bacterial translocation. Perinatal exposure to CPF may therefore have short- and long-term impacts on the digestive tract.

Breakdown of mucin as barrier to digestive enzymes in the ischemic rat small intestine

Loss of integrity of the epithelial/mucosal barrier in the small intestine has been associated with different pathologies that originate and/or develop in the gastrointestinal tract. We showed recently that mucin, the main protein in the mucus layer, is disrupted during early periods of intestinal ischemia. This event is accompanied by entry of pancreatic digestive enzymes into the intestinal wall. We hypothesize that the mucin-containing mucus layer is the main barrier preventing digestive enzymes from contacting the epithelium. Mucin breakdown may render the epithelium accessible to pancreatic enzymes, causing its disruption and increased permeability. The objective of this study was to investigate the role of mucin as a protection for epithelial integrity and function. A rat model of 30 min splanchnic arterial occlusion (SAO) was used to study the degradation of two mucin isoforms (mucin 2 and 13) and two epithelial membrane proteins (E-cadherin and toll-like receptor 4, TLR4). In addition, the role of digestive enzymes in mucin breakdown was assessed in this model by luminal inhibition with acarbose, tranexamic acid, or nafamostat mesilate. Furthermore, the protective effect of the mucin layer against trypsin-mediated disruption of the intestinal epithelium was studied in vitro. Rats after SAO showed degradation of mucin 2 and fragmentation of mucin 13, which was not prevented by protease inhibition. Mucin breakdown was accompanied by increased intestinal permeability to FITC-dextran as well as degradation of E-cadherin and TLR4. Addition of mucin to intestinal epithelial cells in vitro protected against trypsin-mediated degradation of E-cadherin and TLR4 and reduced permeability of FITC-dextran across the monolayer. These results indicate that mucin plays an important role in the preservation of the mucosal barrier and that ischemia but not digestive enzymes disturbs mucin integrity, while digestive enzymes actively mediate epithelial cell disruption.

Intestinal mucus layer preservation in female rats attenuates gut injury after trauma-hemorrhagic shock

BACKGROUND

We tested the hypothesis that females are more resistant to trauma-hemorrhagic shock (T/HS)-induced gut injury than males, and this is related to better preservation of their intestinal mucus layer, which is influenced in turn by the estrus cycle stage at the time of injury.

METHODS

Male, proestrus and diestrus female rats underwent a laparotomy (trauma) and 90 minutes of shock ( approximately 35 mm Hg). At 3 hours after reperfusion, terminal ileum was harvested and stained with Carnoy's Alcian Blue for mucus assessment, hematoxylin and eosin, and periodic acid schiff for villous and goblet cell morphology and injury. Ileal permeability was measured in separate intestinal segments using the ex vivo everted gut sac technique.

RESULTS

When compared with males, proestrus female rats were significantly more resistant to T/HS-induced morphologic gut injury, as reflected in both a lower incidence of villous injury (14% vs. 22%; p < 0.05) and a lesser grade of injury (1.0 vs. 2.8; p < 0.05) as well as preservation of gut barrier function (17.9 vs. 32.2; p < 0.05). This resistance to gut injury was associated with significant preservation of the mucus layer (87% vs. 62%; p < 0.05) and was influenced by the estrus cycle stage of the female rats. There was a significant inverse correlation between mucus layer coverage and the incidence (r = 0.9; p < 0.0001) and magnitude (r = 0.89; p < 0.0001) of villous injury and gut permeability (r = 0.74; p < 0.001).

CONCLUSIONS

The resistance of female rats to T/HS-induced intestinal injury and dysfunction was associated with better preservation of the intestinal mucus barrier and was to some extent estrus cycle-dependent. Preservation of the mucus barrier may protect against shock-induced gut injury and subsequent distant organ injury by limiting the ability of luminal contents such as bacteria and digestive enzymes from coming into direct contact with the epithelium.

Medium-chain triglycerides enhance mucous secretion and cell proliferation in the rat

BACKGROUND

The specific purpose of this study was to investigate the effects of medium-chain triglycerides (MCTs) on intestinal cell proliferation and mucous secretion of the small intestine in the rat.

METHODS

Rats were fed chow diet and given MCTs or the same weight of corn oil (5 g/kg per day) by gavage daily for 2 weeks, and then tissue samples of the small intestines were harvested. Leptin concentration in the small intestine was measured. Cell proliferation and apoptosis in the small intestine was determined by immunohistochemistry. Diamine oxidase (DAO) activity was measured by colorimetric assay.

RESULTS

In rats fed only chow diet (normal rats), the number of goblet cells per villi was 14.2 +/- 0.75 in the jejunum and 15.2 +/- 1.12 in the ileum. The number of goblet cells increased significantly in rats given MCTs compared with rats given corn oil or normal rats. Ki-67-positive cells were detected on the entire villi and the crypts in the small intestine. Furthermore, the proliferative index and the apoptotic index were also significantly greater in rats given MCTs than rats given corn oil or normal rats. Moreover, DAO activity and leptin concentration in the small intestine were significantly greater in rats given MCTs than rats given corn oil or normal rats.

CONCLUSIONS

MCTs enhance cell proliferation of the intestinal epithelium and mucous secretion from goblet cells in the small intestine. These effects may protect the gut in patients suffering from inflammatory bowel disease or enterogenous infection.

Intestinal dendritic cells and epithelial barrier dysfunction in Crohn's disease

Crohn's disease (CD) is a chronic gastrointestinal inflammatory disorder considered to be the result of an inappropriate and exaggerated mucosal immune reaction to yet undefined triggers from the gut flora in genetically predisposed individuals. This inflammatory phenomenon has been characterized by an adaptive T-cell response in addition to an abnormal function of the innate immune system. Dendritic cells (DCs) are constituents of this innate system, inducing T-cell activation via antigen presentation. In the gut, mucosal DCs are separated from the luminal milieu by a monolayer of cylindrical epithelial cells that forms an anatomical and physiological barrier that controls the normal traffic of antigens between both compartments. An imbalance of colonic and ileal DC distribution in tissues from CD patients as well as functional differences between DCs isolated from normal and diseased intestinal samples have been demonstrated. Moreover, a gut barrier defect in the para- and transepithelial routes in addition to a significant reduction in the intestinal secretion of epithelial products involved in barrier function has been well documented in CD. Therefore, this may expose the diseased mucosa to overwhelming amounts of antigens, resulting in abnormal DC activation and a subsequent imbalance in their distribution. In conclusion, this review provides a summary of relevant progress in CD, intestinal epithelial permeability, and DCs highlighting a potential relationship between increased epithelial permeability and abnormal DC distribution during the pathogenesis of intestinal inflammation.

Pancreatic duct ligation abrogates the trauma hemorrhage-induced gut barrier failure and the subsequent production of biologically active intestinal lymph

The studies of the mechanisms by which trauma-hemorrhagic shock leads to gut injury and dysfunction have largely ignored the nonbacterial factors contained within the lumen of the intestine. Yet, there is increasing evidence suggesting that intraluminal pancreatic proteases may be involved in this process. Thus, we tested the hypothesis that pancreatic proteases are necessary for the trauma-hemorrhagic shock-induced gut injury and the production of biologically active mesenteric lymph by determining the extent to which pancreatic duct ligation (PDL) would limit gut injury and mesenteric lymph bioactivity. To assess the effect of PDL on gut injury and dysfunction gut morphology, the mucus layer structure and the gut permeability were measured in the following four groups of male rats subjected to laparotomy (trauma) and hemorrhagic shock (pressure, 30 mmHg for 90 min): (1) rats subjected to trauma plus sham-shock (T/SS), (2) T/SS rats undergoing PDL (T/SS + PDL), (3) rats subjected to trauma and hemorrhagic shock (T/HS), and (4) rats subjected to T/HS + PDL. The ability of mesenteric lymph from these four rat groups to kill endothelial cells and activate neutrophils was tested in vitro. The PDL did not affect any of the parameters studied because there were no differences between the T/SS and the T/SS + PDL groups. However, PDL protected the gut from injury and dysfunction because PDL significantly abrogated T/HS-induced mucosal villous injury, loss of the intestinal mucus layer, and gut permeability. Likewise, PDL totally reversed the endothelial cell cytotoxic activity of T/HS lymph and reduced the ability of T/HS lymph to prime naive neutrophils for an augmented respiratory burst. Thus, it seems that intraluminal pancreatic proteases are necessary for the T/HS-induced gut injury and the production of bioactive mesenteric lymph.

Relationship between disruption of the unstirred mucus layer and intestinal restitution in loss of gut barrier function after trauma hemorrhagic shock

BACKGROUND

The factors involved in shock-induced loss of gut barrier function remain to be defined fully and studies investigating gut injury have focused primarily on the systemic side of the intestine.

METHODS

Male Sprague-Dawley rats were subjected to a laparotomy (trauma) and 90 minutes of trauma sham shock (T/SS) or actual trauma (laparotomy) hemorrhagic shock (T/HS) (30 mm Hg). At 0, 30, 60, or 180 minutes after the end of shock and volume resuscitation (reperfusion), the animals were killed and samples of the ileum were collected for intestinal morphologic analysis, analysis of the unstirred mucus layer, and for barrier function by measuring permeability to flourescein dextran.

RESULTS

T/HS-induced morphologic evidence of mucosal injury as well as epithelial apoptosis was present at the end of the shock period and maximal after 60 minutes of reperfusion. At 3 hours after reperfusion, the degree of villous injury and enterocyte apoptosis had decreased. In contrast to the morphologic appearance of the villi, disruption of the mucus layer became progressively more severe over time and was manifest as a decrease in mucus thickness, progressive loss of coverage of the luminal surface by the mucus layer, and a change in mucus appearance from a dense to a loose structure. Studies of intestinal permeability documented that T/HS-induced loss of gut barrier function persisted throughout the 3-hour reperfusion period and were associated with injury to the mucus layer as well as the villi.

CONCLUSIONS

T/HS leads to changes in the intestinal mucus layer as well as increased villous injury, apoptosis, and gut permeability. Additionally, increased gut permeability was associated with loss of the intestinal mucus layer suggesting that T/HS-induced injury to the mucus layer may contribute to the loss of gut barrier function.

Rôles physiologiques des mucines dans la barrière colique

Colonic mucus is a key element of colonic barrier as it is located at the frontier between luminal microflora and colonic mucosa itself. Colonic mucus is mainly composed of high molecular weight glycoproteins called mucins that can be either secreted or membrane-linked. The expression of various colonic mucins is altered in colorectal cancers or inflammations. The aim of this review is to highlight the crucial role played by colonic mucins in the maintenance of colonic barrier integrity, both because they are part of the protective mucus layer, and because they individually exert specific functions involved in epithelial barrier, like cell growth and differentiation, immunomodulation, signal transduction or cell adhesion.

Chronic stress induces mast cell-dependent bacterial adherence and initiates mucosal inflammation in rat intestine

BACKGROUND & AIMS

Chronic psychological stress is an important factor in relapses of intestinal disorders, but it remains unclear if stress can induce primary gut inflammation in a previously healthy host.

METHODS

Mast cell-deficient (Ws/Ws) rats and wild-type control (+/+) rats were submitted to water avoidance stress or sham stress (1 h/day) for 10 consecutive days, as a model of ongoing life stress.

RESULTS

Both rat groups had similar systemic responses to stress, as assessed by changes in weight, corticosterone levels, and defecation. In +/+ rats, chronic stress induced barrier dysfunction in the ileum and colon (increased macromolecular permeability and depletion of mucus) and ultrastructural changes in epithelial cells (enlarged mitochondria and presence of autophagosomes) associated with bacterial adhesion and penetration into enterocytes. Moreover, hyperplasia and activation of mast cells, infiltration of neutrophils and mononuclear cells, and increased myeloperoxidase (MPO) activity were documented in the mucosa. In intestine of Ws/Ws rats, epithelial function and morphology were unchanged by chronic stress, bacterial-epithelial cell interaction was not demonstrated, and there was no evidence of inflammatory cell infiltration.

CONCLUSIONS

These findings suggest that chronic psychological stress can be an initiating factor in intestinal inflammation by impairing mucosal defenses against luminal bacteria and highlight the importance of mast cells in this process.

Aggregation substance promotes colonic mucosal invasion of Enterococcus faecalis in an ex vivo model

BACKGROUND

Bacterial translocation through the gastrointestinal tract is the crucial step in the pathogenesis of intraabdominal infections. We assessed whether aggregation substance (AS), a bacterial adhesin and virulence factor of Enterococcus faecalis, promotes bacterial translocation and colonic mucosal invasion in an ex vivo experiment.

METHODS

Colonic mucosa of male Wistar rats was placed in a modified Ussing system. The mucosal side of the chamber was filled with a suspension of E. faecalis OG1X:pAM721 (AS-positive) or E. faecalis OG1X (AS-negative). The serosal side was filled with sterile Dulbecco's modified Eagle's medium. For assessment of colonic mucosal invasion the mucosal side was incubated for 2.5 h with a suspension of AS-positive or AS-negative enterococci. After being washed, a solution of gentamicin and penicillin G in tissue culture medium was added on both sides in order to kill extracellular bacteria. Subsequently, the mucosa was removed from the system, washed, lysed with Triton X-100, and homogenized. Viable intramural bacteria were quantified by plating serial dilutions of the homogenate on Todd-Hewitt broth agar plates. To quantify bacterial translocation samples which were taken at various time points from the serosal side were plated on Todd-Hewitt broth agar plates and colony forming units (CFU) were determined.

RESULTS

Invasion of the AS-positive E. faecalis strain OG1X:pAM721 into the colonic mucosa was significantly higher than invasion rates of the AS-negative strain OG1X (2.88 log(10) CFU/ml vs 1.73 log(10) CFU/ml; P = 0.02). However, none of the tested strains was found to translocate from the mucosal to the serosal side within the incubation time of 4 h.

CONCLUSIONS

The aggregation substance promotes invasion of E. faecalis into colonic mucosa.

Cold preservation of the human colon and ileum with University of Wisconsin solution

The inclusion of the colon in the intestinal graft resulted in worsening patient and graft outcome and increased the incidence of infection and rejection. In this study, we examine the role of ischemia on the barrier function of the epithelium during cold ischemia. Samples were collected from 15 harvested and transplanted human donor grafts (colon, 10; ileum, 6), which were immersed in University of Wisconsin (UW) solution. Ischemia (6, 12, 24, and 48 h) and reoxygenation were performed to evaluate the mucosal electrical status using the Ussing chamber technique. The functions of enterocytes and crypt cells were tested by glucose and theophylline challenge. Modified Park's classification was applied to evaluate the severity of mucosal damage under light microscopy. The colon had higher levels of baseline potential difference, short-circuit current, and resistance than the ileum during 6 48 h of ischemia. Colonic epithelial cells responded well to theophylline stimulation at 24 h of ischemia, while there was no ileal response. The colonic mucosa was histopathologically well preserved in UW solution for 48 h, and mucosal damage induced by reoxygenation was less than in the ileum. In conclusion, electrophysiologically and histopathologically, the colon is less susceptible to cold preservation damage than the ileum during storage with UW solution.

Role of intestinal mucus on the uptake of latex beads by Peyer's patches and on their transport to mesenteric lymph nodes in rats

BACKGROUND

The effects of N-acetylcysteine (NAC) as a mucolytic agent on the uptake of fluorescent polystyrene microparticles by Peyer's patches, on intestinal permeability, and on subsequent transport to mesenteric lymph nodes (MLNs) were investigated to establish the role of mucus gel layer in this process.

METHODS

Twenty rats were divided into two groups: control (n = 10) and NAC (n = 10). Fluorescent polystyrene latex beads of 3.2+/-0.2 microm in diameter were used as a probe for measuring the previously mentioned parameters. The solution of latex beads (0.1 mL) was injected into a 2-cm length of ileal loop containing Peyer's patches, with 0.1 mL of saline (control group) or with 0.1 mL of NAC solution (NAC group) within 10 cm proximal from the ileocaecal valve. Intestinal loops, portal blood, and neighboring MLNs were taken within 1 hour of injection. Intestinal sections were stained by periodic acid-Schiff reagent. Peyer's patches and MLNs were analyzed for the count of particles by image analysis using a confocal laser scanning microscope.

RESULTS

Morphologically, periodic acid-Schiff positive uniform mucus gel was present in front of Peyer's patches of the control group, and mucus gel layer was disrupted and noncontinuous in the NAC group. The number of particles within Peyer's patches and MLNs in the NAC group was significantly higher than that in the control group (p<.001). Intestinal permeability of latex beads in the NAC group was significantly higher than that in the control group (p<.001).

CONCLUSIONS

These data suggest that the mucus gel layer located in front of Peyer's patches is one of the important factors for the uptake of noxious macromolecules, and this in turn plays a major role on small intestinal permeability and subsequent translocation to MLNs.

Changes, with age, in the phospholipid content of the intestinal mucus layer of the newborn rabbit

BACKGROUND/PURPOSE

The high incidence of bacterial translocation in newborns is thought to be caused, in part, by the immaturity of the intestinal mucosal barrier. Recently, intestinal mucus phospholipids (PL) have been reported to be important factors in the function of this mucosal barrier. The aim of this study was to quantify changes, with age, in the intestinal mucus PL of the newborn rabbit.

METHODS

Mucus was gently scraped from the small intestinal mucosal surface of rabbits of different ages (0, 7, 14, and 28 days old and adult; n = 6 for all groups). PL was extracted from the mucus and was separated by two-dimensional thin-layer chromatography. The isolated phospholipid spots were quantified for their phosphorus content.

RESULTS

Total PL content of the mucus decreased significantly with age (day 0, 21+/-2; day 7, 16+/-4; day 14, 9+/-3; day 28, 2+/-1; adult, 1+/-1 micromol/g wet mucus; P = .0001). Phosphatidylcholine and phosphatidylethanolamine levels in the adult rabbits were significantly lower in comparison with the 0-, 7-, and 14-day-old pups (P < .05). In contrast, lysophosphatidylcholine and lysophosphatidylethanolamine were significantly higher in the 28-day-old and adult rabbits in comparison with the 0-, 7-, and 14-day-old pups (P < .05). Phosphatidylinositol + phosphatidylserine levels in 7-day-old rabbits was significantly higher compared with adult rabbits. There was no significant difference in the composition of sphingomyeline between groups.

CONCLUSION

Significant changes in the content and composition of the intestinal mucus phospholipids were observed during the first month of life in rabbits.

The effect of epidermal growth factor on the septic complications of acute pancreatitis

Bacterial translocation (BT) from the gastrointestinal tract to mesenteric lymph nodes (MLN) and other extraintestinal organs is an important source of infection in acute pancreatitis (AP). Epidermal growth factor (EGF), a peptide hormone with trophic effects on gut mucosa, has decreased intestinal mucosal injury in septic rats and decreased burn-induced BT in mice. The purpose of this study is to examine whether EGF could affect BT in acute necrotizing pancreatitis. Forty-eight male Sprague-Dawley rats (250-350 g) were studied. AP was induced in Group I and Group II by pressure injection of 3% taurocholate and trypsin into the biliopancreatic duct (1 ml/kg of body weight). Group III and Group IV underwent laparotomy without induction of acute pancreatitis. Group I rats received human recombinant EGF (100 micrograms/kg, subcutaneously twice daily) and Group II rats received a similar volume of 0.1% bovine serum albumin as a placebo postoperatively. Group III and Group IV received EGF and placebo, respectively. At 48 hr postoperatively, blood was drawn for culture and amylase determinations. Jejunum and ileum were obtained to measure mucosal protein content, mucosal thickness, villus height, and crypt depth. Specimens from MLN, spleen, liver, pancreas, and cecum were harvested for pathology and culture of gram positive (G+), gram negative (G-), and anaerobic bacteria. Ileal mucosal protein levels were increased significantly in Group I (1.96 +/- 0.14 mg/cm) compared to Group II (0.95 +/- 0.15 mg/cm intestinal segment) (P < 0.01). Jejunal and ileal mucosal thickness, villus height, and crypt depth in Group I were significantly increased when compared to Group II (P < 0.05). All 12 rats in Group II had BT to MLN compared to 58% (7 of 12 rats) in Group I (P < 0.05). Thirty-three percent (4 of 12 rats) had BT to distant sites such as pancreas, spleen, liver, and/or blood in Group I vs 83% (10 of 12 rats) in Group II (P < 0.05). EGF treatment minimizes intestinal damage, decreases BT to MLN and bacterial spread to distant sites, and may be beneficial in preventing septic complications in AP.

Role of bacterial adherence and the mucus barrier on bacterial translocation: effects of protein malnutrition and endotoxin in rats

OBJECTIVE

The purpose of the study was to investigate the potential relations between mucosal bacterial adherence, intestinal mucus and mucin content, and bacterial translocation.

SUMMARY BACKGROUND DATA

The attachment of bacteria to mucosal surfaces is the initial event in the pathogenesis of most bacterial infections that originate at mucosal surfaces, such as the gut. The intestinal mucus layer appears to function as a defensive barrier limiting micro-organisms present in the intestinal lumen from colonizing enterocytes. Consequently, studies focusing on the biology of bacterial adherence to the intestinal mucosa likely are to be important in clarifying the pathogenesis of gut origin sepsis.

METHODS

To explore the relations between intestinal bacterial adherence, mucus bacterial binding, and bacterial translocation, two models were used. One (protein malnutrition) in which profound alterations in intestinal morphology occurs in the absence of significant translocation and one (endotoxin challenge) in which bacterial translocation occurs and intestinal morphology is relatively normal.

RESULTS

Protein malnutrition was not associated with bacterial translocation and measurement of enteroadherent, mucosally associated bacterial population levels documented that the total number of gram-negative enteric bacilli adherent to the ileum and cecum was less in the protein-malnourished rats than in the normally nourished animals (p < 0.01). Furthermore, there was an inverse relation between the duration of protein malnutrition and bacterial adherence to the intestinal mucosa (r = 0.62, p < 0.002). In contrast, after endotoxin challenge, the level of enteroadherent bacteria was increased and bacterial translocation was observed. The binding of Escherichia coli to immobilized ileal mucus in vitro was decreased significantly in protein-malnourished rats, whereas E. coli binding to insoluble ileal mucus was increased in the rats receiving endotoxin.

CONCLUSIONS

This study indicates that the adherence of bacteria to the intestinal mucosal surface is an important factor in bacterial translocation, that intestinal mucus modulates bacterial adherence, and that increased levels of mucosally associated bacteria are associated with a loss intestinal barrier function to bacteria.

Peritrophic matrix structure and function

Formed of proteins, glycoproteins, and chitin microfibrils in a proteoglycan matrix, the peritrophic matrix (PM) separates the food from the midgut epithelium in most but not all insects. A PM occurs in two forms. A type I PM is delaminated from the entire midgut epithelium and, in some cases, may only be formed in response to feeding and the type of meal ingested. A type II PM is produced by a specialized region of the anterior midgut called the cardia and forms a continuous sleeve (or sleeves) that is always present. As it is positioned between food and midgut epithelium, the PM plays key roles in the intestinal biology of the insect. The PM may protect the midgut epithelium from mechanical damage and insult from pathogens and toxins; it must act as a semipermeable membrane regulating passage of molecules between the different midgut compartments; and it may separate the midgut lumen into different, physiologically significant compartments.

Adhesive mucous gel layer and mucus release as intestinal barrier in rats

BACKGROUND

Although it has been reported that total parenteral nutrition induces an increased intestinal permeability and a decreased mucous gel layer covering the intestinal epithelium, the role of mucous gel on intestinal permeability has not been well understood. We examined the in vivo effects of N-acetyl cysteine (NAC) as mucolytic agent and colchicine as suppressant of the mucus production on the intestinal transmission of fluorescein isothiocyanate dextran 70,000 (FITC-dextran).

METHODS

Rats were divided into four groups. In each group, FITC-dextran (750 mg/kg) with or without NAC (3000 mg/kg) was injected into the small intestinal lumen 3 hours after intraperitoneal injection of saline or colchicine (Col, 10 mg/kg). Thirty minutes after injection of FITC-dextran, blood samples were taken from portal vein to analyze plasma fluorescein concentration by fluorescence spectrometry. Samples of small intestine were sectioned in a cryostat for fluorescence microscopy, and the identical sections were stained by periodic acid-Schiff reaction.

RESULTS

Plasma FITC-dextran level in NAC group was higher than that in control group (p < .01), that in Col + NAC group was higher than that in Col group (p < .01) and that in Col + NAC group was higher than that in NAC group (p < .05). The spaces between villi were filled with mucous gel in the control and Col groups, whereas those were not entirely filled with mucous gel in NAC and Col + NAC groups. FITC-dextran and mucous gel showed complementary distribution in all rats. The villous interstitial edema was recognized in NAC group and the villi were disrupted in Col + NAC group.

CONCLUSIONS

These results suggest that intestinal permeability is possibly affected not only by the mucous gel covering the intestinal epithelium but also by mucus release from goblet cells of the small intestine.