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Oxidants potentiate Ca(2+)- and cAMP-stimulated Cl(-) secretion in intestinal epithelial T84 cells.

BACKGROUND & AIMS: Diarrhea is one of the major complications of inflammatory bowel disease. The role of oxidants in promoting net intestinal secretion is important, but the cellular mechanisms underlying their effects are unclear. We examined the effects and defined the cellular actions of the oxidant monochloramine (NH(2)Cl) on anion secretion in human colonic T84 cells. METHODS: Effects of NH(2)Cl on basal and agonist-stimulated short-circuit current (Isc) of T84 monolayers were determined. Apical Cl(-) and basolateral K(+) conductances were measured by efflux of (125)I(-) and (86)Rb(+), respectively. RESULTS: NH(2)Cl alone had little effect on Isc and (125)I(-) efflux. However, pretreatment with NH(2)Cl led to a concentration-dependent potentiation of the Ca(2+)-mediated Isc and of submaximal cAMP-mediated responses. These effects were associated with increased basolateral K(+) channel conductance and were blocked by increasing cellular Ca(2+) buffering capacity with Quin-2. Whole-cell voltage clamp experiments showed that NH(2)Cl potentiated Ca(2+) activation of basolateral K(+) channel conductance. CONCLUSIONS: Oxidants potentiate both Ca(2+)- and cAMP-stimulated Cl(-) secretion by a direct effect on calcium-activated basolateral K(+) channel conductance, lowering its Ca(2+) activation threshold. This effect may play an important role in amplifying and prolonging the secretory response of inflamed intestinal mucosa and enhancing the severity of diarrhea.

Aminoquinolines↗

Control of synthesis and secretion of intestinal apolipoprotein A-IV by lipid.

Apolipoprotein (apo) A-IV, a component of intestinally secreted, triacylglycerol-rich lipoproteins, has recently been proposed as a physiological controller of gastric function and food intake. Thus, it is important to understand the mechanisms involved in the control of expression, synthesis and secretion of apo A-IV. Apo A-IV is a member of a closely linked, multigene cluster which includes apolipoproteins A-I and C-III. Expression and synthesis of apo A-IV display marked variability with regard to species, tissue, stage of development and response to hormones, but intestinal apo A-IV is consistently stimulated by dietary lipid. The precise molecular mechanisms underlying the response of apo A-IV to lipid have not been clearly defined. Most evidence supports the hypothesis that some aspect of lipid transport is necessary for the apo A-IV response, but only part of this response may be due to a direct effect of intestinal lipid: recent findings suggest a connection between intestinal production of apo A-IV and hormonal and/or neural factors associated with operation of the "ileal brake." Thus, apo A-IV may play an integrative role in the modulation of both upper gastrointestinal function and ingestive behavior.

Animals↗

Effect of base precursors on water and electrolyte transport during oral hydration solution perfusion in secreting rat intestine.

In situ steady-state, single-pass small intestine perfusions in rats were carried out to compare the effect of the bicarbonate and citrate World Health Organization oral rehydration solutions and a base precursor-free solution on intestinal water and electrolyte transport after inducing intestinal secretion with purified heat-stable Escherichia coli enterotoxin. When toxin was not perfused, the rates of water, sodium, and bicarbonate absorption were significantly greater from the bicarbonate-containing solution than from the citrate or base precursor-free solutions. Chloride absorption was greater from the base precursor-free solution, but this might reflect the higher chloride concentration of the perfusate. When toxin was perfused, there was no significant difference among the solutions in the rates of water, potassium, or chloride absorption. Sodium absorption occurred at significantly greater rates from both the bicarbonate and the base precursor-free solutions than from the citrate solution. Base precursor-containing solutions may not provide any advantage over a base precursor-free solution in stimulating water and sodium absorption in 5'-cyclic guanosine monophosphate mediated acute diarrhea.

Administration, Oral↗

Stimulation of specific Aeromonas antibody secretion in rat intestine by gamma-aminobutyric acid.

This study was undertaken to assess a possible role for gamma-aminobutyric acid (GABA) in the regulation of intestinal secretion of IgA and IgG antibodies. Rats were immunized with culture supernatant of Aeromonas hydrophila isolate SSU. This culture supernatant contains a number of toxins that may be considered virulence factors. After 24 days of immunization, rats were anesthetized and a 10-cm intestinal segment was intubated and ligated at both ends in situ. The intestinal loop was perfused with phosphate-buffered saline (PBS). The effluents were collected for measurement of IgA and IgG by the ELISA. When compared with the effect of intravenous administration of normal saline in the control group, intravenous injection of GABA (30 mg/kg) resulted in a significant increase of IgA and IgG secretion in the experimental group. These stimulatory effects of GABA on secretion of IgA and IgG were abolished by bicuculline, a GABA-receptor antagonist, and by atropine, indicating that the GABA-stimulated secretion of IgA and IgG was mediated via the GABA receptors and cholinergic muscarinic receptors. These results suggest that GABA may participate in the nervous regulation of intestinal secretion of IgA and IgG antibodies in the rat.

Aeromonas↗

A putative enzyme from various secretions specifically inhibits antibody-antigen interactions.

Various human secretions (intestinal secretion, saliva, nasal mucus, lacrimal fluid) have been found to inhibit the binding of antibodies to their antigens. Various characteristics (e.g. time, pH, temperature dependence, affinity and size exclusion chromatography) suggested that the inhibitory activity was attributable to an enzyme. Further investigations revealed that this enzyme reacted with the Fab portion of immunoglobulin G, specifically with the heavy chain. It is assumed that it represents a novel immunoglobulin-specific protease since similar results were not obtained with proteolytic enzymes from human digestive organs e.g. pepsin, trypsin and chymotrypsin. Finally, investigating saliva it was demonstrated that the putative protease was not identical to enzymes from periodontal bacteria which are proteolytic for the Fc portion of immunoglobulins. The findings could be of general importance in the design of immunoassays which are to be applied to human (and possibly animal) secretions.

Alkaline Phosphatase↗

Search for the ideal oral rehydration solution: studies in a model of secretory diarrhoea.

In situ perfusion of whole rat small intestine was used to compare the efficacy of five oral rehydration solutions in promoting water and sodium absorption in normal intestine and secreting intestine after exposure to cholera toxin. Solutions varied in their sodium (35-90 mmol/l) and glucose (111-200 mmol/l) concentrations, molar ratio of glucose:sodium (1.2-5.8), and osmolality (281-331 mOsmol/kg), and contained either bicarbonate (18-30 mmol/l) or citrate (10 mmol/l). In normal intestine all solutions promoted net water absorption. Cholera toxin induced reproducible water secretion but all solutions reversed this to absorption. Water absorption was greatest with solutions containing sodium 60 mmol/l and glucose 111 or 140 mmol/l, and with a glucose:sodium ratio approximately 2, in both normal and secreting intestine. All solutions promoted net glucose absorption in both normal and secreting intestine. Net sodium absorption occurred with solutions containing greater than or equal to 60 mmol/l sodium in normal intestine but sodium secretion occurred from all solutions in secreting intestine. Sodium movement was directly related to the sodium concentration of the solution and sodium secretion occurred despite net water and glucose absorption. We consider that these studies may guide future development of oral rehydration solutions.

Animals↗

Factors affecting Caco-2 intestinal epithelial cell interleukin-6 secretion.

Intestinal epithelial cells (IEC) have previously been shown to produce several cytokines including interleukin-6 (IL-6). However, many factors which may regulate IL-6 secretion by human IEC still remain a mystery due in part to the lack of appropriate model cell lines and the difficulty of culturing human IEC over long periods of time. We have determined that the human colonic carcinoma cell line Caco-2 is capable of secreting IL-6 when stimulated by the inflammatory cytokines IL-1beta or tumor necrosis factor-alpha (TNF-alpha), and stimulation of these cells with IL-1beta plus TNF-alpha induced a synergistic enhancement of IL-6 secretion. The inflammatory cytokine-induced enhancement in IL-6 secretion was greatest when the cells were cultured in a 10% CO2 atmosphere as compared to cells grown in 5% CO2, suggesting that environmental CO2 levels may affect IEC cytokine secretion. Finally, long-term culture of the Caco-2 cells to induce cellular differentiation had no effect on the capacity of these cells to produce IL-6, indicating that the regulation of IL-6 secretion was not affected by differentiation. Taken together, these studies provide important information on the factors which regulate IL-6 secretion by human IEC as they may contribute to the cytokine network during a mucosal inflammation. The results also suggest that the Caco-2 cell line is an appropriate model for further studies on the regulation of cytokine secretion by human IEC.

Caco-2 Cells↗

Vasoactive intestinal peptide stimulation of adenylate cyclase and active electrolyte secretion in intestinal mucosa.

Vasoactive intestinal peptide (VIP), originally isolated from hog small intestinal mucosa, has been shown to cause small intestinal secretion. More recently, this peptide has been identified in the plasma and tumors of patients with the so-called "pancreatic cholera" syndrome. In order to explore the possible role of VIP in the pathogenesis of this syndrome, we examined the effects of this peptide and other hormones on the cyclic AMP levels, adenylate cyclase activity, and ion transport in in vitro preparations of ileal mucosa. In rabbit ileal mucosa, VIP (20 mug/ml) caused a prompt fivefold increase in cyclic AMP level, whereas nine other hormones, which have been postulated to cause intestinal secretion, failed to exert such an effect. Pentagastrin and glucagon also failed to increase cyclic AMP levels in canine ileal mucosa. An increase in mucosal cyclic AMP levels was observed at a VIP concentration of 0.1 mug/ml and appeared to be nearly maximal at 2.0 mug/ml. VIP (100 mug/ml) stimulated adenylate cyclase activity in a membrane preparation from rabbit ileal mucosa. Secretin (6.0 x 10(-5) M) failed to do so. When added to the serosal side of isolated rabbit ileal mucosa clamped in an Ussing chamber, VIP (2 mug/ml) increased short-circuit current (SCC) and caused net secretion of both Cl and Na. Net Cl secretion exceeded net Na secretion. These effects of VIP on mucosal cyclic AMP metabolism and ion transport are similar to those observed with cholera enterotoxin and certain prostaglandins. VIP was also tested with normal human ileal mucosa. At a concentration of 2 mug/ml it caused a fivefold increase in cyclic AMP level and an increase in SCC of the same magnitude as that caused by 5 mM theophylline. Addition of a second 2-mug/ml dose of VIP and addition of theophylline after VIP produced no further change in SCC. We conclude the VIP stimulates adenylate cyclase and active ion secretion in both rabbit and human ileal mucosa. This may be related to the pathogenesis of diarrhea in patients with the pancreatic cholera syndrome.

Adenylyl Cyclases↗

Regulation of intestinal proglucagon-derived peptide secretion by intestinal regulatory peptides.

The physiological regulation of intestinal proglucagon-derived peptide secretion has not been well studied. We have therefore used a fetal rat intestinal cell culture model to investigate the control of secretion of the gut glucagon-like immunoreactive (GLI) peptides by other intestinal regulatory peptides in vitro. Secretion of the intestinal GLI peptides was found to be stimulated in a dose-dependent fashion by the intestinal endocrine peptide, gastric inhibitory peptide (at greater than or equal to 10(-10) M, P less than 0.05), and by the neurocrine peptides, gastrin-releasing peptide (at greater than or equal to 10(-12) M, P less than 0.05), and calcitonin gene-related peptide (at greater than or equal to 10(-8) M, P less than 0.05). Gastrin-releasing peptide and its amphibian equivalent, bombesin were equipotent in stimulating GLI peptide secretion. In contrast, the endocrine and neurocrine intestinal somatostatin-related peptides, somatostatin-28 and -14, inhibited release of the GLI peptides, at concentrations of 10(-10) (P less than 0.01) and 10(-8) (P less than 0.01) M, respectively, with significant differences in potency between the two peptides detected at 10(-10) M (P less than 0.05). The inhibitory effects of both somatostatin-28 and -14 could be blocked by preincubation of the cells with pertussis toxin (P less than 0.05). Dose-dependent stimulation of gut GLI peptide secretion was also detected in response to treatment of cultured cells with sodium oleate (at 10(-4) M; P less than 0.05), or with the cholinergic agonist bethanecol (at greater than or equal to 100 microM; P less than 0.05). Other endocrine [cholecystokinin, glucagon, glucagon-like peptide-1(1-37), glucagon-like peptide-1(7-37), glucagon-like peptide-2, neurotensin, and peptide YY] and neurocrine (vasoactive intestinal peptide) peptides, and the synthetic glucocorticoid, dexamethasone, were without effect on secretion of the gut GLI peptides, at doses of 10(-12) to 10(-6) M. The results of the present study therefore demonstrate that secretion of the intestinal proglucagon-derived peptides is under the regulatory control of a wide variety of intestinal endocrine and neurocrine peptides, as well as nutrients (fats) and neurotransmitters (acetylcholine).

Animal Nutritional Physiological Phenomena↗

The importance of the enteric nervous system for the bile-salt-induced secretion in the small intestine of the rat.

We have investigated the possible involvement of the enteric nervous system in the intestinal secretion induced by sodium deoxycholate. Hexamethonium, lidocaine, and tetrodotoxin significantly inhibited the fluid secretion in extrinsically innervated and denervated rat jejunal segments. Atropine had no effect. We conclude that the sodium-deoxycholate-induced intestinal secretion is partly caused by the activation of local nervous reflexes.

Animals↗

Evolutionary aspects of intestinal bicarbonate secretion in fish.

Experiments compared intestinal HCO3- secretion in the intestine of marine teleost Gulf toadfish, Opsanus beta, to representatives of early chondrostean and chondrichthyan fishes, the Siberian sturgeon, Acipenser baerii, and white-spotted bamboo shark, Chiloscyllium plagiosum, respectively. As seen in marine teleosts, luminal HCO3- concentrations were 10-fold plasma levels in all species when exposed to hyperosmotic conditions. While intestinal water absorption left Mg2+ and SO4(2-) concentrated in intestinal fluids up to four-fold ambient seawater concentrations, HCO3- was concentrated up to 50 times ambient levels as a result of intestinal HCO3- secretion. Reduced luminal Cl- concentrations in the intestine of all species suggest that HCO3- secretion also occurs via Cl-/HCO3- exchange in chondrostean and chondrichthyan fishes. Sturgeon began precipitating carbonates from the gut after only 3 days at 14 per thousand, a mechanism utilized by marine teleosts to reduce intestinal fluid osmolality and maintain calcium homeostasis. Analysis of published intestinal fluid composition in the cyclostome Lampetra fluviatilis reveals that this species likely also utilize intestinal HCO3- secretion for osmoregulation. Analysis of existing cyclostome data and our results indicate that intestinal Cl-/HCO3- exchange plays an integral role in maintaining hydromineral balance not only in teleosts, but in all fish (and perhaps other animals) with a need to drink seawater.

Animals↗

[The meaning of duodenostasis in the intestinal phase gastric secretion disorders in bleeding duodenal ulcer].

The data on the duodenal motor-evacuational function investigation in 62 patients with an ulcer bleeding are presented. It was established that the degree of duodenal chronic impassability is correlating with the degree of disorders of the gastric secretion intestinal phase. That's why it is necessary to stipulate the elimination of hyperchlorhydria in all phases of gastric secretion while such complication correction.

Adult↗

Secretion rate of intestinal immunoglobulins, complement factor C3, "acute phase" reactants, and albumin in the perfused ileum and jejunum of normal man.

A new method for assessment of the intestinal secretion rate of immunoglobulins and other proteins is evaluated. The procedure involves a combination of luminal perfusion of a defined intestinal segment and analysis of the aspirated perfusates by rocket immunoelectrophoresis. The technique is sensitive and reliable. A material from the normal human jejunum and ileum is presented. The method is proposed as an investigative tool for characterization of the local immunological system of the small intestine.

Adult↗

Spontaneous secretion from the dog small intestine in vivo.

Forty loops of small intestine in the dog were perfused under control conditions with a balanced electrolyte solution. Most of the loops absorbed sodium and water, but 10 loops were in a state of spontaneous intestinal secretion. Compared to absorbing loops, spontaneously secreting loops exhibited reduced values for lumen-to-plasma fluxes of sodium and chloride and increased values for the plasma-to-lumen fluxes of these ions. Analysis of flux ratios suggested that sodium and chloride were actively scecreted during spontaneous intestinal secretion in the dog. Spontaneous secretion was similar to the secretion induced by CT or VIP, except that the latter were associated with a change in PD whereas the PD in the spontaneously secreting loops was the same as in the spontaneously absorbing loops.

Animals↗