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PubMed1991

Inhibition of anaphylaxis-evoked intestinal fluid secretion by the dual application of an H1 antagonist and cyclooxygenase inhibitor.

The regulation of anaphylaxis-mediated fluid secretion by the small intestine was examined in rats immunized by infection with Trichinella spiralis and reinfected by intraduodenal injection with L1 larvae. Net fluid secretion, which was measured as the volume of fluid present in the intestine 30 minutes after the challenge infection, was significantly greater in both actively and passively immunized rats than in nonimmune rats. The amount of fluid recovered from the immune host was equivalent to that secreted in response to 50 micrograms/kg of prostaglandin E2 or 250 micrograms/kg of cholera toxin. Worm-induced fluid secretion in immune hosts was reduced by treatment with diphenhydramine and inhibited by the dual application of diphenhydramine and indomethacin. Indomethacin alone had no effect despite inhibiting mucosal prostaglandin synthesis. Fluid secretion was unaltered by prior treatment of immune rats with a 5-lipoxygenase inhibitor, L-651,392, and only slightly reduced when L-651,392 was used in combination with indomethacin. After a challenge infection, more histamine was released into intestinal loops of immune rats than those of nonimmune rats. Prechallenge treatment of immune rats with indomethacin caused a twofold increase in histamine release. In summary, anaphylaxis-induced fluid secretion in the small intestine is mediated largely by histamine and cyclooxygenase products. This secretion can be lowered by treatment with diphenhydramine and further reduced by diphenhydramine in combination with indomethacin. The paradoxical effects of indomethacin when used alone and in combination with diphenhydramine are explained by the downregulation of histamine release by products of the cyclooxygenase pathway.

Analysis of Variance↗
PubMed2005

The role of epithelial P2Y2 and P2Y4 receptors in the regulation of intestinal chloride secretion.

UTP-induced chloride secretion by the intestinal mucosa mounted in Ussing chambers was assessed by measurement of the short-circuit current (I(sc)) in the presence of phloridzin in the case of jejunum or amiloride in the case of colon to eliminate any contribution of electrogenic Na(+) movement to the net ionic transport. Since we have previously demonstrated the absence of chloride-secretory response to apical UTP in the jejunum from P2Y(4)-null mice, in the present study we studied the response to basolateral UTP in the jejunum and to either apical or basolateral UTP in the colon, in both P2Y(2)- and P2Y(4)-deficient mice. In the jejunum, the chloride-secretory response to basolateral UTP was partially reduced in both P2Y(2)- (40%) and P2Y(4)- (60%) null mice. In the colon, both apical or basolateral UTP increased the I(sc). That response was abolished in a chloride-free medium. The colonic chloride-secretory response to either basolateral or apical UTP was abolished in P2Y(4)-deficient mice, but not significantly affected in P2Y(2)-deficient mice. The chloride-secretory response to forskolin was potentiated by prior basolateral addition of UTP and this potentiation was abolished in P2Y(4)-null mice. The jejunum of mice homozygous for the DeltaF508 mutation of cystic fibrosis transmembrane conductance regulator was responsive to UTP, but the magnitude of that response was smaller than in the wild-type littermates. In conclusion, the P2Y(4) receptor fully mediates the chloride-secretory response to UTP in both small and large intestines, except at the basolateral side of the jejunum, where both P2Y(2) and P2Y(4) receptors are involved.

Animals↗
PubMed2001

Retinyl ester secretion by intestinal cells: a specific and regulated process dependent on assembly and secretion of chylomicrons.

Retinyl esters (RE) have been used extensively as markers to study chylomicron (CM) catabolism because they are secreted in the postprandial state with CM and do not exchange with other lipoproteins in the plasma. To understand the mechanism of secretion of RE by the intestine under the fasting and postprandial states, differentiated Caco-2 cells were supplemented with radiolabeled retinol under conditions that support or do not support CM secretion. We observed that these cells assimilate vitamin A by a rapid uptake mechanism. After uptake, cells store retinol in both esterified and unesterified forms. Under fasting conditions, cells do not secrete RE but secrete free retinol unassociated with lipoproteins. Under postprandial conditions, cells secrete significant amounts of RE only with CM. The secretion of RE with CM was independent of the rate of uptake of retinol and intracellular free and esterified retinol levels, and was absolutely dependent on the assembly and secretion of CM. The secretion of RE was correlated with the secretion of CM and not with the secretion of total apolipoprotein B. Inhibition of CM secretion by Pluronic L81 decreased the secretion of RE and did not result in their increased secretion with smaller lipoproteins. These data strongly suggest that RE secretion by the intestinal cells is a specific and regulated process that occurs in the postprandial state and is dependent on the assembly and secretion of CM. We propose that RE are added to CM during final stages of lipoprotein assembly and may serve as signposts for these steps.

Caco-2 Cells↗
PubMed1998

Regulation of mucosal B cell immunoglobulin secretion by intestinal epithelial cell-derived cytokines.

Intestinal epithelial cells (IEC) secrete a variety of cytokines and, because of their close proximity to B cells in the lamina propria, may affect local antibody production via these cytokines. However, studies have not yet addressed which and to what extent these IEC-derived cytokines may affect B cell antibody production. In this study, rat mesenteric lymph node B cells were cultured with culture supernatants from the rat IEC-6 intestinal epithelial cell line to determine their effect on immunoglobulin (Ig) secretion. Unstimulated IEC-6 cells were found to secrete sufficient levels of IL-6 to enhance IgA, IgG and IgM secretion by unstimulated B cells. However, culture of lipopolysaccharide (LPS)-stimulated B cells with the unstimulated IEC-6 supernatant resulted in an enhancement of IgA secretion while IgM secretion was significantly suppressed. Depletion of the IEC-6 supernatant using cytokine specific antibodies revealed that both interleukin 6 (IL-6) and transforming growth factor beta (TGF-beta) were responsible for the enhanced IgA secretion while TGF-beta suppressed IgM secretion. More importantly, culture supernatants from LPS stimulated IEC-6 cells contained enhanced levels of IL-6 which enhanced both IgG and IgA production and partially overcame the suppressive effect of TGF-beta on IgM secretion. These results suggest that intestinal epithelial cells may secrete IL-6 and TGF-beta to regulate local B cell antibody secretion and their effect may be highly dependent upon the activation state of the epithelial cells.

Animals↗
PubMed1987

Evidence for regulation of human colonic mucosal immunoglobulin secretion by intestinal lymphoid cells.

In vitro immunoglobulin secretion has been studied using isolated colonic mucosal lymphoid cell populations obtained from 41 patients with non-inflammatory intestinal disease. Cell fractions were separated into intra-epithelial and lamina propria-enriched populations. The secretion of immunoglobulins by mucosal cells appeared to be independent of mitogen stimulation. When intra-epithelial lymphocyte preparations were co-cultured with autologous lamina propria lymphocytes, the secretion of IgM was significantly depressed but that of IgA and IgG was preserved. Co-cultured of mucosal cells with autologous peripheral blood lymphocytes resulted in suppression of pokeweed mitogen stimulated and unstimulated immunoglobulin secretion. Lamina propria T cells were shown to provide helper function for the in vitro secretion of IgA and IgM but not IgG, by autologous peripheral blood B cells. Immunoglobulin secretion by lamina propria lymphocytes was shown to be partly dependent on the concentration of E-rosette forming cells. These experiments demonstrate that human colonic mucosal lymphoid cells contain specific populations of helper and suppressor cells which selectively control intestinal immunoglobulin secretion.

Biopsy↗
PubMed2006

Mechanisms of net chloride secretion during rotavirus diarrhea in young rabbits: do intestinal villi secrete chloride?

Rotaviral diarrheal illness is one of the most common infectious diseases in children worldwide, but our understanding of its pathophysiology is limited. This study examines whether the enhanced net chloride secretion during rotavirus infection in young rabbits may occur as a result of hypersecretion in crypt cells that would exceed the substantial Cl(-) reabsorption observed in villi. By using a rapid filtration technique, we evaluated transport of (36)Cl and D-(14)C glucose across brush border membrane (BBM) vesicles purified from villus tip and crypt cells isolated in parallel from the entire small intestine. Rotavirus infection impaired SGLT1-mediated Na(+)-D-glucose symport activity in both villus and crypt cell BBM, hence contributing to the massive water loss along the cryptvillus axis. In the same BBM preparations, rotavirus failed to stimulate the Cl(-) transport activities (Cl(-)/H(+) symport, Cl(-)/anion exchange and voltage-activated Cl(-) conductance) at the crypt level, but not at the villus level, questioning, therefore, the origin of net chloride secretion. We propose that the chloride carrier might function in both normal (absorption) and reversed (secretion) modes in villi, depending on the direction of the chloride electrochemical gradient resulting from rotavirus infection, agreeing with our results that rotavirus accelerated both Cl(-) influx and Cl(-) efflux rates across villi BBM.

Animals↗
PubMed1994

Dynamic role of microfilaments in intestinal chloride secretion.

The importance of microfilaments in the regulation of chloride (Cl-) secretion by the human intestinal cell line T84 was investigated using the cytoskeletal probe phalloidin to bind and stabilize F-actin. Phalloidin was found to inhibit secretion mediated by cyclic adenosine monophosphate (cAMP) and the sustained secretory response to the calcium (Ca+2) ionophore ionomycin but not to affect the transient Ca+2-mediated response to carbachol and histamine. Fluorescent microscopic examination of F-actin revealed regionally restricted microfilament remodeling in cAMP- and ionomycin-treated cells. Normal regulation of apical Cl- and basolateral potassium (K+) channel functions was evident in phalloidin-loaded cells. It is concluded that prevention of cytoskeletal remodeling by actin stabilization inhibits the generation of a sustained Cl- secretory response by a mechanism that does not involve Cl- or K+ channels. Depolymerization of F-actin plays an integral role in the regulation of intestinal Cl- secretion.

Actin Cytoskeleton↗
PubMed1994

Oophorectomy in young rats impairs calcium balance by increasing intestinal calcium secretion.

Calcium balance and its major components (true calcium absorption, urinary calcium excretion and intestinal calcium secretion) were assessed by a 6-d balance technique in young (6-wk-old) rats fed a diet containing 7.2 g Ca/kg diet. Following either oophorectomy (oophx) or sham operation, the balance study was repeated at 9, 12 and 15 wk of age. Calcium balance decreased with age but remained positive in each group [mean (pooled SEM): sham, (6 wk) 0.86 to (15 wk) 0.27 (0.03) mmol/d (P < 0.0001); oophx, (6 wk) 0.91 to (15 wk) 0.22 (0.03) mmol/d (P < 0.0001)]. Analysis of variance of the change in calcium balance indicated that there was a significantly greater reduction in calcium balance in the oophx group compared with the sham-operated group. Intestinal calcium absorption decreased in each group with age [sham: (6 wk) 46.3% to (15 wk) 22.6% (1.5%) (P < 0.0001); oophx: (6 wk) 48.2% to (15 wk) 21.2% (1.5%) (P < 0.0001)]. There was a marked rise in intestinal calcium secretion in the oophx group compared with the sham-operated group at 6 wk post-operation (12 wk of age) [oophx: 0.33 (0.02) mmol/d; sham: 0.23 (0.02) mmol/d (P < 0.01)]. Urinary calcium excretion was not affected by either age or oophorectomy. We conclude that oophorectomy in young rats leads to a reduction in calcium accumulation, which is mainly the result of an increase in intestinal calcium secretion.

Aging↗
PubMed1992

Actions of serotonin antagonists on cholera-toxin-induced intestinal fluid secretion.

The effects of several 5-hydroxytryptamine (5-HT) receptor antagonists were tested in rats in vivo on the intestinal fluid secretion evoked by cholera toxin. Five receptor antagonists were used, namely 2-bromolysergic acid diethylamine (2-bromo-LSD), granisetron, ketanserin, methysergide and ondansetron. The drugs were used in doses that inhibited the arterial hypertension and/or bradycardia evoked by 5-HT given i.v. Granisetron and ondansetron markedly diminished cholera-toxin-evoked secretion, whereas ketanserin was without any effect. Methysergide also diminished cholera-toxin-induced fluid secretion particularly when the drug was given as an i.v. infusion. The results are considered in relation to the pathophysiology of cholera secretion and to the current views of receptor subtypes for 5-HT. It is proposed that the receptor involved is a 5-HT3 receptor, possibly also a receptor of the 5-HT1 type. Results from experiments in which 5-HT (20 mM) was placed in the intestinal lumen to evoke an intestinal secretion suggest that the 5-HT3 receptor is located in the villus tissue. It was also demonstrated that zimeldine, an inhibitor of presynaptic 5-HT reuptake, diminished choleraic secretion, an effect that may be ascribed to a 5-HT tachyphylaxis caused by an accumulation of 5-HT in a synaptic cleft.

Animals↗
PubMed1993

[Effect of Y-25130, a selective 5-HT3 receptor antagonist, on the intestinal fluid secretion in rats].

We studied the effect of Y-25130 on the intestinal fluid secretion induced by 5-HT and cholera toxin in rats. 1) Net fluid secretion was increased dose-dependently by intramesenteric artery infusion of 5-HT (1-10 micrograms/min). 2) Y-25130 (0.01-1 mg/kg, i.v.) inhibited the net fluid secretion induced by 5-HT (3 micrograms/min). Granisetron and ondansetron also inhibited the net fluid secretion induced by 5-HT. 3) Methysergide did not inhibit the fluid secretion, and neither atropine nor tetrodotoxin inhibited it. 4) Cholera toxin (1-10 micrograms/2 ml into jejunal loops) caused profuse net fluid secretion. 5) Y-25130 (1 mg/kg, i.v.) inhibited the net fluid secretion induced by cholera toxin (3 micrograms/2 ml). Granisetron was inhibitory and ondansetron tended to inhibit the cholera toxin-induced secretion. These results suggest that 5-HT may increase the net fluid secretion through 5-HT3 receptors, and cholera toxin-induced fluid secretion may be at least partially mediated by 5-HT3 receptors. It is expected that Y-25130 may be useful for treating secretory diarrhea in humans.

Animals↗
PubMed1996

Bacteriological method for detecting small intestinal hypomotility.

OBJECTIVE: Small intestinal hypomotility is an important cause of small intestinal bacterial overgrowth, yet assessment of small intestinal motility in this setting is problematic. This study was performed to investigate the validity of a bacteriological method for detecting small intestinal hypomotility. METHODS: Twenty-five subjects without previous gastric surgery were studied with (i) concurrent bacteriological analyses of fasting saliva and gastric and proximal small intestinal aspirates, (ii) measurement of gastric pH, and (iii) scintigraphic assessment of small intestinal transit rates of a liquid test meal. The reproducibility of bacteriological analyses of saliva and small intestinal secretions was determined in 12 subjects. RESULTS: Serial bacteriological analyses of saliva and proximal small intestinal secretions yielded reproducible results over time periods of up to 1 month. Eleven subjects were deemed to harbor Enterobacteriaceae of nonsalivary origin in proximal small intestinal secretions. Orocaecal transit, but not gastric emptying, of a liquid test meal was significantly delayed in this group (p = 0.002 and p = 0.84, respectively), suggesting the presence of small intestinal hypomotility. Impaired gastric acidity unlikely confounded assessment of the origin of small intestinal Enterobacteriaceae in any instance. CONCLUSIONS: The presence of Enterobacteriaceae of nonsalivary origin in proximal small intestinal secretions may be taken to reflect the presence of small intestinal hypomotility. The presence of impaired gastric acidity does not confound this approach. Because small intestinal intubation and culture of aspirate are required anyway to accurately diagnose small intestinal bacterial overgrowth, the simple addition of concurrent bacteriological analysis of saliva may allow small intestinal hypomotility to be detected at the same time as the presence or absence of small intestinal bacterial overgrowth itself is established, thus streamlining the investigation of subjects for this disorder and its possible causes.

Bacterial Infections↗
PubMed1998

Short-chain fatty acids regulate IGF-binding protein secretion by intestinal epithelial cells.

Gastrointestinal epithelial cells secrete insulin-like growth factor (IGF)-binding proteins (IGFBPs), which modulate the actions of IGFs on cell proliferation and differentiation. Short-chain fatty acids are bacterial metabolites from unabsorbed carbohydrate (including fiber). We hypothesized that they may alter the pattern of IGFBPs secreted by epithelial cells as part of a wider phenomenon by which luminal molecules regulate gastrointestinal epithelial cell signaling. The intestinal epithelial cell line, Caco-2, predominantly secretes IGFBP-3; however, butyrate increased the secretion of IGFBP-2 in a dose-dependent and reversible manner. Butyrate decreased the secretion of IGFBP-3. Butyrate altered only the synthesis and not the cell sorting of IGFBPs because 1) the secretion of IGFBPs remained polarized despite changes in their rates of production, and 2) IGFBP secretion corresponded to mRNA accumulation. The ability of short-chain fatty acids or the fungicide trichostatin A to stimulate IGFBP-2 correlated with their actions on histone acetylation. In conclusion, intestinal epithelial cells respond to short-chain fatty acids by altering secretion of IGFBPs.

Adenocarcinoma↗
PubMed2000

Intestinal mucosal secretion of basic fibroblast growth factor in patients with ulcerative colitis.

BACKGROUND: Basic fibroblast growth factor (bFGF) promotes angiogenesis and several other biologic processes, including proliferation of mesenchymal cells and tumor progression. We investigated whether bFGF could be detected in the intraluminal secretion of the small intestine, sigmoid colon, and rectum in healthy individuals and in patients with ulcerative colitis. METHODS: We used endoscopic perfusion techniques to obtain samples from well-defined intestinal segments. The perfusion fluid concentrations of bFGF, biochemical markers of inflammation, myeloperoxidase (MPO), interleukin-6 (IL-6), and permeability (albumin) were determined with immunochemical methods. RESULTS: In the perfusion fluids the albumin concentration, which reflects passive diffusion, was less than 1% of the plasma concentration, whereas the intestinal concentration of bFGF was similar to that in plasma. Among healthy subjects the concentration of bFGF was eightfold higher in the jejunum and twofold higher in the rectum than in the sigmoid colon. The perfusion fluid from colorectal segments in patients with ulcerative colitis had a significantly higher mean concentration of bFGF than that from healthy individuals; an almost 10-fold difference was found in rectal segments. There were strong correlations between the concentration of bFGF and the concentrations of MPO and IL-6. CONCLUSIONS: The high concentrations of bFGF in the intestinal perfusion fluid reflect either a local synthesis or an active secretion of bFGF within the mucosa. The bFGF concentration differs in intestinal anatomic location and increases significantly in patients with ulcerative colitis in close relationship with biochemical markers of inflammation and permeability.

Adult↗
PubMed1984

The effects of intravenous phosphate loading on salivary phosphorus secretion, net intestinal phosphorus absorption and pathway of excretion in sheep fed roughage diets.

Mature sheep fitted with rumen and duodenal cannulae and fed either pelleted hay or grass diets were given supplementary phosphorus by continuous intravenous infusion and the effects on salivary phosphorus secretion, intestinal phosphorus absorption and pathway of excretion were studied. In control periods little phosphorus was excreted in the urine, the faeces being the major pathway for excretion. Infusion of phosphorus increased both urine and faecal phosphorus excretion though in sheep fed the hay diet the urine response was much less marked than in those fed the grass diet. This was not due to differences in plasma phosphate levels but rather to differences in renal tubular reabsorptive efficiency, though the reason for this is at present unclear. Intravenous phosphate loading had little effect on salivary phosphorus secretion, most of the increase in faecal phosphorus excretion being the result of reduced reabsorption within the intestine. The significance of these changes in relation to the control of phosphorus balance in ruminants is discussed.

Absorption↗
PubMed1976

Stimulated flow of pancreatic and biliary secretions after intestinal exposure to cholera toxin.

1. Duodeno-jejunal intestinal loops in rats were perfused with cholera toxin and the pancreatic and biliary secretory responses studied. 2. Intraluminal cholera toxin induced a significant flow of pancreatic and biliary fluid and sustained protein (enzyme) secretion in pancreatic juice, in addition to the expected stimulation of mucosal secretion. 3. Intravenously injected cholera toxin failed to elicit a secretory flow from the pancreas and biliary tract. 4. The time-course of the enhanced secretory flow from pancreas and biliary tract after intraluminal cholera toxin corresponds closely to the secretion of intestinal fluid. 5. The results of these studies provide evidence of sustained stimulation of pancreatic and biliary secretions after mucosal exposure to cholera toxin. These observations support the suggestion that secretion from the pancreas and liver may significantly contribute to the total intestinal secretion in cholera.

Animals↗
PubMed1999

Myosin regulation of NKCC1: effects on cAMP-mediated Cl- secretion in intestinal epithelia.

The basally located actin cytoskeleton has been demonstrated previously to regulate Cl- secretion from intestinal epithelia via its effects on the Na+-K+-2Cl- cotransporter (NKCC1). In nontransporting epithelia, inhibition of myosin light chain kinase (MLCK) prevents cell-shrinkage-induced activation of NKCC1. The aim of this study was to investigate the role of myosin in the regulation of secretagogue-stimulated Cl- secretion in intestinal epithelia. The human intestinal epithelial cell line T84 was used for these studies. Prevention of myosin light chain phosphorylation with the MLCK inhibitor ML-9 or ML-7 and inhibition of myosin ATPase with butanedione monoxime (BDM) attenuated cAMP but not Ca2+-mediated Cl- secretion. Both ML-9 and BDM diminished cAMP activation of NKCC1. Neither apical Cl- channel activity, basolateral K+ channel activity, nor Na+-K+-ATPase were affected by these agents. Cytochalasin D prevented such attenuation. cAMP-induced rearrangement of basal actin microfilaments was prevented by both ML-9 and BDM. The phosphorylation of mosin light chain and subsequent contraction of basal actin-myosin bundles are crucial to the cAMP-driven activation of NKCC1 and subsequent apical Cl- efflux.

Actins↗
PubMed1982

Cholinergic stimulation of immunoglobulin A secretion in rat intestine.

This study was undertaken to assess a possible role for cholinergic agents in the regulation of intestinal immunoglobulin A secretion. Intestinal loops, constructed in anesthetized rats, were perfused with phosphate buffered normal saline. Immunoglobulin A concentrations were measured by radioimmunoassay. When compared with the effect of normal saline in the same rats, intravenous injection of pilocarpine, 10 mg/kg, increased immunoglobulin A concentrations in perfusates from ileal loops (p less than 0.001). Qualitatively similar results were obtained with muscarine and bethanechol, from jejunal and colonic loops, and from unanesthetized rats. Immunoglobulin A concentrations increased four- to eightfold during maximal cholinergic stimulation. Atropine, 250 micrograms intravenously, completely blocked the effect of pilocarpine on immunoglobulin A secretion (p less than 0.005), and also inhibited basal intestinal immunoglobulin A secretion for 40 min after injection. As determined on 10%-40% sucrose density gradients, much of the immunoglobulin A secreted after cholinergic stimulation sedimented in the 11S range. These data indicate that intestinal secretion of immunoglobulin A is stimulated by the muscarinic effect of cholinergic agonists, and suggest that basal secretion of immunoglobulin A may be influenced by the parasympathetic nervous system.

Anesthesia, General↗