Duodenal Epithelium Research Articles

Electrophysiological characteristics of the Necturus proximal duodenal mucosa: effects of ion substitutions.

Voltage-sensitive glass micro-electrodes were used to determine the electrical characteristics of Necturus proximal duodenal epithelium. Some comparative experiments with amiloride were performed with gastric antrum. The apical and the basolateral cell membrane potential differences in duodenum averaged -32 mV and -34 mV (cell negative) respectively. The transepithelial potential difference was -2 mV (lumen negative). The EMF across the apical cell membrane was -29 mV and that across the basolateral cell membrane -39 mV. The transepithelial resistance (Rt) of 63 omega cm2 and the paracellular pathway resistance (Rs) of 80 omega cm2 are of magnitudes similar to that previously reported for more distal amphibian small intestine. The apical and basolateral cell membrane resistances, however, were lower than those reported for distal small intestine. Ion permeabilities for Na+, K+ and Cl- across the apical cell membrane were calculated from ion substitution experiments. The permeability sequence across the apical cell membrane was PK:PCl:PNa 3.02:1.31:1.00. Luminal amiloride (10(-4)M) was without significant effect, further indicating a low duodenal membrane conductance for Na+. The low conductances for K+, Na+ and Cl- suggest that the major ion transport modes across the apical duodenal cell membrane are electroneutral in nature. In contrast, amiloride caused a marked increase in the transmembrane potentials in the antrum.

Pharmacokinetic profile of RU 41740, a bacterial immunomodulator, in mice, rats, and monkeys

A study of the intestinal transport, tissue distribution, metabolism and excretion of RU 41740 (trade name Biostim), an immunomodulating compound given to patients prone to chronic bronchitis, was carried out in mice, rats, and monkeys. This pharmacokinetic study is of value in determining the mode of action of an orally administered biological response modifier on the immune system. Tissue localisation in the duodenal epithelium of C3H axenic mice was performed by an indirect immunofluorescence method; the plasma kinetics, the tissue distribution, and the excretion were assessed using tritiated RU 41740. The metabolites were examined by gel filtration of the circulating products. RU 41740 was found to be present in the lamina propria of duodenal villi 2 h after oral administration and maximum radioactivity was found in the systemic circulation of rats and monkeys from 1 to 4 h after treatment; small amounts of the administered dose were recovered (0.3%) at that time. The absorption was 6.9% of the administered dose in the rat and 1.8–2.1% in the monkey (from plasma kinetics data collected over 14 days). The elution profile of the tritiated circulating product indicated that RU 41740 was modified. Radioactivity was found associated mainly with molecular weight fragments of less than 10,000. The time course distribution of RU 41740 showed that 3 h after treatment, the radioactivity was mainly in the digestive tract, the liver, and the kidneys; later (24 h), it increased in the lung, spleen, mesenteric lymph nodes, adrenals, and ovaries. The excretion route of the radioactivity was predominantly fecal. The presence of RU 41740 fragments in the intestinal tissue, the systemic circulation, and some other tissues may contribute to direct activation of the immune cells localised in the gut, liver, lungs, and so partly explain the immunomodulatory properties of RU 41740.

Immunohistochemical evidence for a lack of ferritin in duodenal absorptive epithelial cells in idiopathic hemochromatosis

Patients with idiopathic hemochromatosis exhibit an unexplained increase in intestinal iron absorption. The aim of this work was to study immunohistochemical H- and L-ferritin distribution in duodenal mucosal cells of patients with idiopathic hemochromatosis, and of subjects with various degrees of iron loading. Biopsy sections of gastrointestinal mucosa from 24 patients with idiopathic hemochromatosis, 10 patients with secondary iron overload, 6 normal subjects, and 13 iron-deficient subjects were analyzed with monoclonal antibodies for the presence of immunohistochemical H and L ferritin types, and with Perls' stain for hemosiderin. Ferritin content of duodenal homogenates was evaluated in 5 cases. The absorptive duodenal cells were found to contain ferritin, mostly of the L type, in apical granules; these ferritin granules were present in all normal, iron-deficient, and iron-over-loaded subjects, but were absent in 21 (87%) of the patients with established idiopathic hemochromatosis. In cells other than those of the duodenal epithelium, such as lamina propria or antral mucosa, ferritin and hemosiderin contents were related to iron loading and no difference was evident between primary and secondary iron overload. These findings indicate that (a) idiopathic hemochromatosis is associated with an altered ferritin expression in the duodenal absorptive epithelial cells, (b) this alteration cannot be detected by analysis of duodenal homogenates, (c) idiopathic hemochromatosis does not affect ferritin accumulation in the other cell types analyzed, and (d) ferritin in absorptive duodenal cells may have a regulatory role in iron absorption.

Distributions of Actin, Vinculin and Fibronectin in the Duodenum of Developing Chick Embryos: Immunohistochemical Studies at the Light Microscope Level: (chick embryo/duodenal morphogenesis/immunofluorescent staining/actin/vinculin).

Microscopic studies were made on the localizations of three different cytoskeletal proteins, actin, vinculin and fibronectin, in the duodenum of developing chick embryos and chicks by an indirect immuno-fluorescent staining method with specific antibodies. Topographical changes in the distributions of these three proteins seemed to be related to stages in morphogenesis of the duodenum. In early stages of embryonic development, findings suggested interaction between actin and vinculin in the apical region of epithelial cells and between actin and fibronectin in the basal region of these cells. From this stage, vinculin and fibronectin seemed to be of importance in determination and continuity of the polarity of the duodenal epithelium, and in control of the intracellular arrangement of actin. This relation between actin and vinculin seemed to continue throughout embryogenesis. The main role of actin in epithelial cells seemed to change on day 12 from that of forming constricting bundles for morphogenesis of previllous ridges to that of microfilaments in the microvilli and the terminal web.

Ultrastructural silver enhancement of Prussian blue-reactive iron in hematopoietic and intestinal cells.

Prussian blue has been widely used to localize iron in a variety of tissues at the light and electron microscopic level. In the present study, thin sections of human marrow and blood cells and rat duodenal cells were exposed to silver proteinate (SP) after staining en bloc with acid ferrocyanide (AF), with and without prior iron saturation using iron nitrilotriacetate (FeNTA). Silver deposition was observed over Prussian blue-reactive sites and significantly enhanced sites of minimal AF and FeNTA-AF staining. AF-SP stain deposits were present in the cytoplasmic matrix, granules, and occasionally on the surfaces of macrophages, monocytes, and erythroblasts. FeNTA-AF-SP stained additional cytoplasmic and surface sites in erythroblasts and stained neutrophil granules intensely. Duodenal epithelium from iron-loaded rats demonstrated strong AF-SP staining of ferric iron in microvilli, apical cytoplasmic matrix, and lateral membranes. Similar preparations from iron-replete rats stained sparsely; however, intense AF-SP staining was observed after iron saturation with FeNTA. SP similarly enhanced luminal ferrous iron deposits stained with acid ferricyanide in rats given intraluminal ferrous iron. AF-SP stain deposits were removed by exposure of thin sections to NH4OH, KCN, or HNO3 but were not affected by prior exposure to HIO4 or NaBH4, consistent with a silver cyanide or complex stain precipitate rather than reduced silver or silver ferriferrocyanide. SP enhancement of Prussian blue allows identification of reactive sites not readily visualized with AF or FeNTA-AF alone, and offers the potential for differentiating AF staining from other deposits or organelles of comparable density.

Mechanisms of acid disposal and acid-stimulated alkaline secretion by gastroduodenal mucosa.

This paper investigates acid disposal by gastric and duodenal mucosa with particular reference to the mechanisms of acid-stimulated luminal alkalinization in the duodenum. The bulk of solute flux across duodenal epithelium occurs by paracellular permeation, and passive diffusion of HCO3 via shunt pathways contributes substantially to luminal alkalinization by this tissue in vitro. Effects on epithelial permeability of two treatments which stimulate mucosal alkaline secretion (PGE2 and low luminal pH) were studied in vivo by measuring transmucosal fluxes of radiolabeled urea (mol wt 76) and inulin (mol wt approximately 5000). Rats were anesthetized and rates of alkalinization in segments of distal duodenum perfused with saline were monitored by continuous titration. PGE2 (10 microM, topically) increased alkaline secretion from 1.63 +/- 0.34 to 3.07 +/- 0.54 microeq/cm/hr (mean +/- SEM, N = 5). Luminal acid exposure (10 mM HCl for 10 min) increased alkalinization rate from 1.54 +/- 0.43 to 2.69 +/- 0.76; subsequent addition of PGE2 induced a further rise to 3.27 +/- 0.54. Recovery of inulin in the luminal perfusate following intravenous injection was less than 10% of that of urea. Topical PGE2 had little or no effect on recovery of either marker. Luminal acidification increased the rate of appearance of urea by 130 +/- 30% (P less than 0.01, N = 6); recovery of inulin rose slightly but did not achieve statistical significance compared with control. Thus stimulation of mucosal alkaline secretion by luminal PGE2 or acid are associated with differential effects on mucosal permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Lysozyme localization in human gastric and duodenal epithelium. An immunocytochemical study.

The distribution of lysozyme in normal gastric and duodenal mucosa was studied by light- and electron-microscopic immunocytochemical techniques (direct enzyme-labeled antibody method). In the duodenal mucosa, lysozyme was found in the Paneth cells and the epithelial cells of Brunner's glands. Electron-microscopically, lysozyme was found in rough endoplasmic reticulum and perinuclear spaces, which were assumed to be protein-synthesizing organelles, and also in the secretory granules of Paneth cells. Additionally, lysozyme was detected in the stomach in mucinous granules and in some parts of the rough endoplasmic reticulum within the epithelial cells of the pyloric glands, the mucous neck cells of the fundic glands, and in several surface epithelial cells of the plyoric and fundic regions. This suggests that some quantity of lysozyme in gastrointestinal secretion originates from the gastric and duodenal glands, and that it acts as a defense mechanism in the gastrointestinal tract.

Pyloric gastrin-producing cells and pyloric sphincter muscle cells are nuclear targets for 3H 1,25(OH)2 vitamin D3. Studied by autoradiography and immunohistochemistry.

Autoradiographic studies were conducted to identify and characterize target cells for 1,25(OH)2 vitamin D3 in the pyloric region of rats and mice. After injection of 3H 1,25(OH)2 vitamin D3, nuclear concentration of radioactivity was observed in nuclei of duodenal epithelium and certain cells of pyloric glands, while most of the epithelial cells in the pyloric and gastric glands did not show nuclear labeling. In combined immunohistochemical studies, cells in the pyloric glands that showed nuclear concentration of radioactivity, were stained in their cytoplasm with antibodies to gastrin. Also, cells of the pyloric sphincter muscle showed nuclear labeling, in contrast to cells of the duodenal muscularis, which remained unlabeled under the conditions of the experiments. The results indicate that the cells with nuclear radioactivity contain receptors for 1,25(OH)2 vitamin D3 and suggest that gastrin secretion and pyloric muscle functions are regulated by a direct action of 1,25(OH)2 vitamin D3 on these cells.

Influence of hormones on glycogen and glucose metabolism in embryonic chick intestine.

Previous studies on the development of embryonic intestine in vitro have revealed a stimulation of epithelial differentiation by the hormones hydrocortisone (HC) and thyroxine (T4). To determine whether these hormones also influence epithelial metabolism, duodena from 14-day-old chicken embryos were cultured for 72 h in the absence of hormones (controls) or in the presence of 1 nM T4 or 1 microM HC. In control cultures, glycogen accumulated within the duodenal epithelium to the level found at 17 days in vivo. T4 reduced glycogen accumulation to 34% of control values, whereas HC increased epithelial glycogen content by 45%. These hormonal effects were due, in part, to modulation of glycogen degradation. In T4 cultures, glucose oxidation activities within the epithelial layer and submucosal tissue were 300 and 140% of control values, respectively, and glucose utilization (removal from the culture medium) was increased. HC significantly decreased both glucose oxidation activity within the submucosal tissue and glucose utilization. These results are consistent with the hypothesis that HC regulates the early phase of epithelial differentiation that is characterized by low metabolic rate and accumulation of energy stores, whereas T4 elicits the prehatching phase of differentiation that is correlated with an increase in metabolic rate and utilization of stored products.

Chronic fluoride toxicity: a scanning electron microscopic study of duodenal mucosa.

The effects of chronic fluoride toxicity on duodenal mucosa of rabbits were investigated using scanning electronmicroscope on materials obtained from rabbits subjected to oral administration of sodium fluoride at the dose of 10 mg/kg body weight per day for a period of 24 months. Significant morphological abnormalities were observed in the mucosa of all the fluoride treated animals [n = 9] when compared to that of control rabbits. The surface of the microvilli of duodenal epithelium revealed a "cracked-clay" appearance in fluoride treated rabbits. Besides, abrasion on the villus surface due to epithelial cell degeneration was also noticed. Mucus probably coating the degenerated cells formed strands over the villi in fluoride treated animals.

Cell Differentiation during Pancreatic Carcinogenesis

In many tissues, carcinogenesis mimics embryonic development. This is true for the pancreas. The first alteration seen during pancreatic tumor induction in the hamster model is proliferation of poorly differentiated ductular (tubular) structures intermingled with endocrine cells, a pattern consistent with findings in the embryonic and fetal pancreas. However, unlike the fetal tissue, various cell types of intestinal epithelium appear in the advance stages of pancreatic carcinogenesis. Moreover, contrary to the situation in the fetal and adult hamster pancreas, the induced pancreatic lesion expresses antigens with human blood group type specificities, including A, B, H, Leb, Lex, and Ley, antigens that are expressed, however, by fetal and adult duodenal epithelium. Considering the origin of the pancreas from the duodenal mucosa, the overall findings indicate that during pancreatic carcinogenesis some genes, acquired from the progenitor (duodenal) cells, which are inactive in embryonic and normal pancreatic cells, are activated, possibly as a function of some oncogenes. Comparative studies in human tissue lead to the same conclusion.

Intestinal absorption of RU 41740, an immunomodulating compound extracted from Klebsiella pneumoniae, across duodenal epithelium and Peyer's patches of the rabbit

The intestinal transport and degradation of RU 41740, an immunomodulating compound, were tested in vitro across rabbit duodenal epithelium and Peyer's patches mounted in Ussing chambers. Quantification of transport and metabolic behaviour across the intestinal wall were examined using tritiated RU 41740 ([ 3H]RU 41740). The viability of the tissues was assessed by recording electrical parameters. Transepithelial [ 3H]RU 41740-equivalent fluxes from mucosa to serosa were determined and the intracellular catabolism was examined by gel filtration of serosal [ 3H]products on a Sephacryl S-300 column after 2 h of experimentation. Steady-state transport rates were obtained after 60 min; transepithelial fluxes of [ 3H]RU 41740 equivalents were greater across the duodenum than the Peyer's patches (1647 ± 277 ng · h −1 · cm −2 versus 357 ± 61 ng · h −1 · cm −2). Elution profiles of the tritiated-degraded products in the serosal compartment indicated that the radioactivity was mainly associated with low molecular weight fragments (mol. wt. < 10,000) in the duodenum, whereas higher molecular weight fragments were found in the Peyer's patches. These results indicate that RU 41740, like most macromolecules, is transported across the intestinal epithelium by endocytosis with subsequent extensive degradation probably at the lysosomal level. However, the minor fraction transported intact as well as under high molecular weight products in the Peyer's patches might have an important effect on the underlying immune system.

Rapid action of 1,25-dihydroxyvitamin D3 on calcium transport in perfused chick duodenum: effect of inhibitors.

Transport of 45Ca from the lumen to the venous effluent was studied in duodena of normal, vitamin D3-replete (+D) chicks perfused through the celiac artery with 130 pM 1,25(OH)2D3 or vehicle. Administration of actinomycin D 3 h prior to perfusion did not alter the unstimulated transport rate or diminish the response to exogenous 1,25(OH)2D3: After 40 min exposure to the seco-steroid, 45Ca in the vascular effluent was 140% of control levels. The anti-microfilament agent cytochalasin b and the ionophore monensin, an inhibitor of Golgi function, similarly failed to suppress 1,25(OH)2D3-stimulated calcium transport. In pilot studies, Golgi and basal-lateral membrane fractions were prepared from duodenal epithelium of vitamin D-deficient (-D) chicks treated with vehicle or 650 pmol of 1,25(OH)2D3 in vivo 2 h, 10 h, or 15 h before sacrifice, as well as from +D birds. Analyses of Golgi fractions for cathepsin B (CB) activity revealed a biphasic response with time, increasing to 200% of -D levels 2 h after 1,25(OH)2D3 administration and in equivalent preparations from +D birds. Less pronounced increases in acid phosphatase activity were observed in the same membrane fractions. In basal-lateral membranes, enhanced CB activity was detectable 10 h after 1,25(OH)2D3 in vivo, rose to 155% of -D levels at 15 h, and to 245% of controls in fractions from +D birds, whereas acid phosphatase was 75%, 81%, and 125% of controls, respectively, at these times.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of proton and bicarbonate transport in pancreatic cell function.

pancreas the release into the duodenum of digestive enzymes dissolved in an alkaline, HC03 -rich fluid. The HC03 in the pancreatic fluid neutralizes the gastric acid content, which is important in preventing acid damage to the duodenal epithelium. Two main aspects of the role of HCO; and H+ transport in the pancreas have been studied. First. the role of HC03 in the secretion of fluid by the pancreatic ducts has been extensively studied. Many of these studies were carried out at the organ level, some of these were at the level of the isolated main duct. Only a few studies were performed on ductular cells because of their inaccessibility and the problems encountered in isolating ducts or ductu­ lar cells due to the small volume fraction of these cells in the pancreas (less than 4%). Second, a limited number of studies have been dedicated to the role of HC03 transport in the Ca2+ -dependent secretion of enzymes and fluid by the acinar cells. In this chapter we focus on the mechanism of H+ -HCO; transport and its relation to the transport of other ions by the ductular cells, and we briefly summarize the literature on the role of H+ and HCO; transport in the acinar cells.

Demonstration of epidermal growth factor binding sites in the adult rat small intestine by autoradiography

The distribution of epidermal growth factor (EGF) receptors was studied in the distal portion of duodenum using light microscopic autoradiography performed at different time intervals (2–60 min) after intravenous injection of 125I-labelled EGF into adult rats. The results revealed a substantial binding of EGF to both cell types of the mucosal epithelium in duodenal crypts and villi, the columnar absorptive cells and the globet cells. Labelling was also found over few cells of lamina propria. No labelling was observed over the striated border of the duodenal mucosa epithelium. The time-course study performed in epithelial cells of duodenal crypts and villi showed that most silver grains were found at the periphery of the cells 2 min after injection. At the 7 min, silver grains were found both at the periphery and over the cytoplasm, more specifically the supranuclear region of the columnar absorptive cells. The number of grains overlying the cytoplasm of these cells was markedly reduced at 60 min. By quantitative autoradiography, maximal values were reached 7 min after the injection. Control experiments indicated that the autoradiography reaction was due to specific interaction of 125I-labelled EGF with its receptor. These results clearly indicate that EGF receptors are present in epithelial cells of the duodenal mucosa and suggest that the radioactive tracer is taken up by these cells.

Role of thyroxine and insulin on the development of the fetal mouse duodenum in organ culture.

The role of thyroxine and insulin in the regulation of proliferation and differentiation of the immature duodenal epithelium of the fetal mouse was investigated using an organ culture method with a serum-free medium. Thyroxine (10 nM) stimulates specifically the activity of maltase. Insulin (125 mU/mL) remains without effect on the maturation of all hydrolytic functions studied. Each hormone significantly increases the percentages of brush border enzyme activities liberated in the medium and reduces the amount of glucose released in the medium. In the presence of dexamethasone (76 nM) the effect of thyroxine on maltase activity is still observed. Finally, thyroxine and insulin do not modify the labelling index in the duodenal crypts of the explants in the presence or absence of dexamethasone. These findings indicate that thyroxine and insulin can act directly on the development of the fetal mouse duodenum at the end of gestation. Nevertheless, their implication in prenatal development of the gut functions appears to be of minor importance.

Regulation of duodenal Ca2+ pump by calmodulin and vitamin D-dependent Ca2+-binding protein

The Ca2+ pump in rat duodenal epithelium is studied as ATP-dependent Ca2+ uptake in a vesicle preparation with a 9-fold purification in Na+-K+-ATPase activity and a 20-fold purification of Na+-K+-ATPase with respect to an endoplasmic reticulum marker. ATP-dependent Ca2+ uptake is reduced by 60% by digitonin treatment of the vesicles, whereas high-affinity Ca2+-ATPase is stimulated by the same treatment. Different methods to deplete membrane preparations of calmodulin have been used. In EDTA osmotically shocked vesicles, calmodulin stimulated ATP-dependent Ca2+ transport up to 100% in a Ca2+ concentration-dependent manner. The duodenal Ca2+ pump is inhibited by calmodulin antagonists only at low Ca2+ concentrations and in membranes not depleted from calmodulin. Vitamin D-dependent Ca2+-binding protein (Mr = 10,000) in concentrations up to 5 microM did not affect the rate of ATP-dependent Ca2+ transport, either in Ca2+-EGTA-buffered solutions or in EGTA-free solutions. In membrane preparations from vitamin D-deficient rats, the effects of calmodulin and of Ca2+-binding protein were identical to the vitamin D-repleted control preparations. This excludes a specific effect of Ca2+-binding protein and calmodulin in the vitamin D dependency of duodenal Ca2+-ATPase.

Phytol and Peroxisome Proliferation

Infantile Refsum's disease is characterized by high levels of phytanic acid and the absence of normal hepatic peroxisomes. We investigated the in vivo influence of phytol, a precursor of phytanic acid, on peroxisomes by both biochemical and morphological methods. Enhanced supply of phytol in the diet of adult mice causes proliferation of hepatic peroxisomes. The peroxisomal beta-oxidizing capacity as well as exchanges of acyl moieties between peroxisomes and mitochondria are raised around 5- and 2-fold, respectively. In parallel a 1.5-fold increase of total catalase and mitochondrial butyryl-CoA dehydrogenase activities occurs, whereas peroxisomal urate oxidase and glycolate oxidase remain normally active. Serum triglyceride levels are decreased after 3 wk of phytol feeding; serum cholesterol levels remain unaffected. Phytol feeding also induces peroxisome proliferation in duodenal epithelium, in myocardium and in skin sebaceous glands, but not in kidney.

Effects of Indomethacin on the Duodenal Mucosa of Rats: Comparative Study with Cysteamine

Effects of indomethacin and cysteamine on the duodenal mucosa of rats were studied microscopically (using scanning electron microscopy) and also functionally. Indomethacin (5 mg/kg, s.c.) induced no microscopic damage to the duodenal epithelium for up to 6 hr after administration. Indomethacin had no effects on gastric H+ output and the amount of H+ in the duodenum, but did reduce the duodenal HCO3− secretion (both basal and 10 mM-HCl stimulated). PGE2 contents in the duodenal mucosa were markedly reduced by indomethacin for 6 hr. These results suggest that reductions of duodenal HCO3− secretion and endogenous prostaglandins per se do not impair the H+ disposal system of the duodenum and so do not damage the epithelial cells. In contrast, cysteamine (100 mg/kg, s.c.) produced microscopic damage to the duodenal epithelium as early as 2 hr later. Cysteamine significantly increased gastric H+ output and reduced duodenal HCO3− secretion, resulting in an increased amount of H+ in the duodenum 3 hr later. Cysteamine had no effect on PGE2 contents in the duodenum. The time lag between damage formation and functional changes suggests that the earliest damage caused by cysteamine occurs by mechanisms other than erosive action of H+ emptied by the stomach. The increased amount of H+ may contribute to an enhancement of the initial damage.

Energy Costs of Ion Pumping by Animal Tissues

Results from recent in vitro studies indicate that in excess of 20% of the energy expenditure of skeletal muscle, duodenal epithelium and liver of domestic ruminants is to achieve Na+ and K+ transport across the plasma membrane. The energy cost of active Ca2+ transport is less clear but is likely less than 10% of the total expenditure of skeletal muscle at rest. Energy expenditure on Na+ and K+ transport was quite sensitive to the physiological state of the animal. During lactation, Na+ and K+ transport accounted for nearly half of the in vitro O2 uptake of skeletal muscle, duodenal epithelium and liver. The energetic cost of supporting Na+ and K+ transport was also elevated in young, as compared with older animals, by feed intake and by exposure to cold. Na+ and K+ transport appears to be a substantial component of the maintenance energy expenditure of ruminant tissues. Its variation, therefore, implies that change of maintenance energy expenditures with physiological state of the animal warrants serious attention.