Endothelin-1 induces mucosal mast cell degranulation in the rat small intestine

The enhanced production of endothelial cell-derived vasoactive mediators and the activation of mast cells (MCs) have been implicated in the pathogenesis of mucosal damage during ischemia and reperfusion injuries. The first objective of our study was to define the in vivo relation between endothelin-1 (ET-1) and the MC system. Secondly, we determined whether pretreatment with ET receptor antagonists would attenuate MC responses to exogenous ET-1. In the first series of experiments, increasing doses of ET-1 (0. 1, 1 and 3 nmol/kg i.v.) were administered to anesthetized rats. In the second series, the animals were pretreated with equimolar doses of the ET-A receptor antagonist BQ-610 or ETR-P1/fl peptide, and the ET-B receptor antagonist IRL-1038. Intestinal perfusion changes and macrohemodynamics were recorded, and the proportion of degranulated MCs was determined in ileal biopsies. The average mucosal thickness was recorded with an image analysis system. ET-1 induced dose-dependent alterations in the hemodynamic and morphological parameters and caused pronounced mucosal injury, with a significant reduction in villus height. The ratio of degranulated MCs was similar in all ET-treated groups (77%, 82% and 86%) to that observed in animals subjected to 15-min ischemia and 60-min reperfusion (85% degranulation). Pretreatment with BQ-610 and ETR-P1/fl peptide attenuated the ET-1 induced alterations in the hemodynamic parameters and decreased structural injury to the mucosa. ET-induced MC degranulation was significantly inhibited by the ET-A receptor antagonists, but not by IRL-1038. These results indicate that elevated levels of circulating ET-1 might induce intestinal mucosal tissue injury and MC degranulation via activation of ET-A receptors, and raise the possibility that ET-A receptor antagonist administration could exert a potentially beneficial effect through a mechanism other than the blockade of vasoconstriction in pathologies associated with an increased ET-1 release.     

The effect of the hookworm Ancylostoma ceylanicum on the mucosal architecture of the small intestine in hamsters

Hookworms are known to cause marked changes to the intestinal mucosa, especially in relation to erosion of the villi. However, since the development of enteropathy has not been examined thoroughly through quantitative experiments on infected animals, the results of experiments conducted in hamsters infected with Ancylostoma ceylanicum are reported. Changes to intestinal architecture were first apparent between 12 and 14 days after infection, and then increased in intensity for 3-4 weeks, persisting for as long as worms were present (>63 days). Following infection, the height of villi declined from a mean of 1002 micro m in na?ve controls to less than 200 micro m and as low as 18 micro m in one case. The depth of the crypts of Lieberkuhn increased from a baseline value of 166 micro m in na?ve controls to in excess of 600 micro m within 6 weeks of infection. Mitotic figures had a baseline value of 5.5 per villus-crypt unit, and this rose to in excess of 25 in some experiments. Changes were dependent on the intensity of the parasite burden on day 20, but by 30 days after infection changes in all three values were maximal and density-dependent relationships were no longer clearly apparent. Villus height and crypt depth returned to near normal values within a week of the removal of worms, although group means for both remained different from na?ve controls for at least 3 weeks after treatment. Cellular division, as reflected in numbers of mitotic figures, stayed elevated for over 5 weeks after removal of worms. The results suggest that enteropathy in hookworm infections stems from a combination of intestinal immune responses and from the grazing activities of the adult worms on the mucosal surface, but is not sufficient per se for expulsion of this parasite.     

Enzymes in the mucosal layer of the small intestine

It has been demonstrated by the methods of histochemical and biochemical examination of the activity of the enzymes that the mucus layer covering the small intestinal wall contains active enzymes (alkaline phosphatase, leucin aminopeptidase IV, saccharase, lactase) and pancreatic enzymes (alpha-amylase and trypsin). Emphasis is laid on the enrichment of the mucus layer with pancreatic enzymes as compared with small intestinal juice. A hypothesis has been advanced according to which the mucus layer undergoes degradation of polymeric and oligomeric substrates, which plays a physiological part in the digestion of nutritive substances and protection of the internal medium against immunoactive biopolymers. The digestion occurring in the mucus layer is proposed to be called mucus digestion.     

Alterations of epithelial layer after ischemic preconditioning of small intestine in rats

Ischemic-reperfusion (IR) injury of the small intestine makes a serious complications associated with various surgical procedures and is related to changes in motility, secretory activity and structural alterations. Preconditioning can reduce range of this damage. The aim of the experimental study was to determine the influence of ischemic preconditioning (IPC) on IR injury on jejunal epithelial layer. Wistar rats (n = 56) were divided in two experimental groups. IR group was subjected to 60 min ischemia of cranial mesenteric artery and followed by reperfusion periods: 1,4,8,24 h (IR1, IR4, IR8, IR24). Group with ischemic preconditioning (IPC+IR) was subjected to two subsequent ischemic attacks (12 min) with 10 min of reperfusion between them, and after 2nd attack ischemia was induced for 60 min followed by relevant reperfusion period. IPC showed the protective impact on the jejunal tissue architecture after 1 h reperfusion, when in IR1 group the highest and significant damage was observed (p < 0.001) in contrast to IPC+IR1 group. Histopathological damage of the intestine in pretreated groups was postponed to 4 h of reperfusion. Protective effect of IPC together with later accumulation of injury signs were confirmed by weaker impact on goblet cell (p < 0.001) and Paneth cell populations (p < 0.05).The increased cells proliferation in preconditioned groups came later, but stronger after 8 h of reperfusion (p < 0.001) and after 24 h of reperfusion still remained at the high activity level (p < 0.001). Our experimental results on the histopathological changes in the jejunum during ischemic preconditioning proved that IPC may have a positive effect on maintaining intestinal barrier function.     

Intestinal mucosal morphometry and ileal epithelial renewal in conventional and germ-free rats fed an amylomaize starch diet.

Intestinal mucosal morphometry and ileal epithelial renewal were studied in conventional (CV) and germ-free (GF) rats fed either poorly digestible amylomaize or normal maize starch diets. Intestinal morphometry and position of labelled enterocytes were studied at various times after tritiated thymidine injection. With amylomaize starch diet, no difference was observed in the size of crypts (C), villi (V) and C + V between duodenum and jejunum both in CV and GF rats. In the ileum, however, values were significantly lower than those in the duodenum and jejunum. Furthermore, the presence of the microbial flora led to higher values when compared with GF values. Despite the morphological modifications in the ileum, no significant difference was detected in the labelled cell positions and epithelial renewal time between CV and GF values. This suggests that the resistant part of amylomaize starch was responsible for the modification in mucosal morphometry and the longer ileal epithelium renewal time in CV rats which then becomes similar to that in GF rats.     

Trichostrongylus colubriformis: epithelial cell kinetics in the small intestine of infected rabbits

Epithelial cell kinetic parameters were compared in intestines of control and Trichostrongylus colubriformis infected rabbits using a microdissection and metaphase accumulation technique in regions of gut with heavy (proximal site) and small (distal site) burdens of worms. In control animals, the cell production rates were respectively 4.3 cells/crypt/hr in the proximal region and 3.7 cells/crypt/hr in the distal one; and the influx of cells onto villi were respectively 67.5 cells/hr and 37.4 cells/hr. In the parasitized rabbits, in the main site of infection, a fourfold increase was recorded in the cell proliferation rate and in the influx of cells onto villi. In the region distal to the main site of infection, the same parameters were twice the control values, although only a low number of T. colubriformis were recovered from this part of gut. These large modifications in the epithelial renewal probably underlies the morphological and enzymological changes previously described in both parts of the T. colubriformis infected gut.     

Proliferation, not apoptosis, alters epithelial cell migration in small intestine of CFTR null mice

Expression of a mutated cystic fibrosis transmembrane conductance regulator (CFTR) has been shown to enhance proliferation within CF airways, and cells expressing a mutated CFTR have been shown to be less susceptible to apoptosis. Because the CFTR is expressed in the epithelial cells lining the gastrointestinal tract and all CF mouse models are characterized by gastrointestinal obstruction, we hypothesized that CFTR null mice would have increased epithelial cell proliferation and reduced apoptosis within the small intestine. The rate of intestinal epithelial cell migration from crypt to villus was increased in CFTR null mice relative to mice expressing the wild-type CFTR. This difference in migration could be explained by an increase in epithelial cell proliferation but not by a difference in apoptosis within the crypts of Lieberkühn. In addition, using two independent sets of CF cell lines, we found that epithelial cell susceptibility to apoptosis was unrelated to the presence of a functional CFTR. Thus increased proliferation but not alterations in apoptosis within epithelial cells might contribute to the pathophysiology of CF.     

Phosphofructokinase D from the epithelial cells of rat small intestine.

Phosphofructokinase from the epithelial cells of rat small intestine was characterized with respect to isoenzyme type in a comparison of its properties with those of the skeletal-muscle, brain and major liver isoenzymes by using five different techniques, namely electrophoresis on cellulose acetate and in polyacrylamide gels, chromatography on DEAE-cellulose, (NH4)2SO4 precipitation and immunotitration. When precautions were taken to inhibit the formation of active proteolytic artifacts by the action of endogenous proteinases, each technique revealed that rat intestinal mucosa contains only a single form of phosphofructokinase. The mucosal isoenzyme was found to be very similar to, although not identical with, the major liver isoenzyme and to be quite distinct from the skeletal-muscle isoenzyme when studied by the techniques of cellulose acetate electrophoresis, chromatography on DEAE-cellulose and immunotitration, whereas the converse was true when studied by the techniques of (NH4)2SO4 precipitation and polyacrylamide-gel electrophoresis. The mucosal isoenzyme was distinct from the brain isoenzyme when studied by each of the five techniques. Tsai & Kemp [(1973) J. Biol. Chem. 248, 785-792] reported that animal tissues contain three principal isoenzymes of phosphofructokinase, type A found as the sole isoenzyme in skeletal muscle, type B found as the major isoenzyme in liver and type C found as a significant isoenzyme in brain. Phosphofructokinase from mucosa is distinct from each of these isoenzymes. Following the nomenclature of Tsai & Kemp (1973), the isoenzyme from the mucosa of rat intestinal epithelial cells is designated phosphofructokinase D. The mucosal and liver isoenzymes behave so similarly with respect to their charge and immunological characteristics, on which the typing of isoenzymes is conventionally based, that it is likely that some tissues reported to contain the liver isoenzyme contain instead the mucosal isoenzyme.     

Intracellular distribution of beta-galactosidases in mucosal cells from hog small intestine.

1. Intracellular distribution of three types of beta-galactosidases (beta-D-galactoside galactohydrolase EC 3.2.1.12) i.e. hetero beta-galactosidase, lactase and acid beta-galactosidase, was studied by examining the properties of subcellular fractions isolated by a systematic fractionation of mucosal cells of the small intestine of the hog. Localization of hetero beta-galactosidase in cytosol could be shown. 2. Localization of lactase in the brush borders was shown by analyzing the purified brush borders prepared separately. 3. To domonstrate the lysosomal localization of acid belta-galactosidase, lysosomes were purified separately and their extract was chromatographed on a hydroxylapatite column. The activities of various enzymes in the purified lysosomes as well as in the intermediary fractions obtained during lysosome purification and the pattern of the hydroxylapatite chromatography led us to conclude that acid beta-galactosidase is a lysosomal enzyme.     

Ammonia production by the small intestine of the rat.

1. Slices of duodenum and jejunum produce ammonia from glutamine in vitro. 2. Ammoniagenesis does not increase in response to acidosis or potassium deficiency, two conditions known to cause enhanced ammoniagenesis in the kidney. 3. Gut contains glutaminase 1 as well as gamma-glutamyl transpeptidase. 4. These enzymes do not show any increase during starvation.     

Acid hydrolases in the suckling rat small intestine I. Fractionation of mucosal homogenates

Synopsis Small intestine mucosal homogenates of suckling rats have been fractionated by centrifugation and analyzed for acid hydrolases and for biochemical markers of subcellular organelles. The results indicate that the acid hydrolases are associated with particles having sedimentation properties similar to those of mitochrondria. The acid hydrolases exhibited latent activity. Subfractionation on a continuous density gradient of sucrose in deuterium oxide demonstrated that these enzymes are associated with particles distinct from other subcellular organelles. Electron micrographs of the acid hydrolase-rich region of the gradient show the presence of numerous small electron dense bodies bounded by a unit membrane.     

The effect of bile and of sodium taurocholate on the epithelial cell dynamics of the rat small intestine.

The absence of bile from the intestinal lumen of rats for a period of 48 hr led to: a decreased proliferative cell pool, reduced cell shedding, and a 50% decrease of the labeling index in the ileum. The constant duodenal perfusion of Na taurocholate for periods of 48, 60, 72, and 96 hr in animals with a biliary diversion was associated with: deepening of crypts and decreased crypt/villus ratios as well as with acceleration of the epithelial cell migration rate on the crypt-villus units. The data suggest that bile and bile acids constitute important regulatory factors influencing enterocyte proliferation, migration and loss.