Duodenal Bicarbonate Research Articles

Особливості періодичної активності шлунка за умов дисбалансу NO-ергічної системи

Nitric oxide is the main inhibitory mediator of the gastrointestinal smooth muscles’ relaxation which stimulates duodenal mucus and bicarbonate secretion. More recent studies have demonstrated that NO also protected the gastrointestinal tract by inhibiting gastric acid secretion. In this study we investigated gastric secretory and motor activity considering the NO imbalance condition. The experiments were carried out on male white laboratory rats (200–230 g). The control group was treated with 0.9% NaCl solution. The injections of NO donator (1.5 mg/kg of 0.1% (Sigma-Aldrich) sodium nitroprusside solution) were made in the second and the third groups during 6 and 12 days. The fourth and the fifth group were treated with NO synthesis inhibitor (40 mg/kg of 1% solution (Sigma-Aldrich) Nω-nitro-L-arginine) during 6 and 12 days respectively. Recording of gastric myoelectric activity (GMA) and gastric juice collection were carried out under anesthesia (ketamine, 110 mg/kg). Next, its volume, pH, glycoprotein and pepsin were measured. Within 6-days stimulation of NO excess decreased gastric juice volume by 47% and increased pH compared to control samples. Pepsin level increased by 62% and glycoprotein level decreased by 68% compared to the checkpoint. After 6 days of L-NNA injections we observed the increase of gastric juice secretion volume (78%) and pH level, however, pepsin concentration remained unchanged. Glycoprotein level increased by 21% compared to control samples. After 12 day NO synthesis inhibitor injections gastric secretion volume increased by 85%. Gastric juice pH level was 200% higher than the control value and exceeded gastric juice pH level (62%) in the third group. In addition, pepsin level tended to decrease when NO deficiency simulation was prolonged. Glycoprotein level decreased by 41% compared to control samples and by 51% compared to the third group. Pepsin level decreased after 12 day NO-inhibitor injections as gastric juice pH level increased. After 12 day Na-nitroprusside treatment, gastric myoelectric index decreased by 42% compared to the checkpoint. The type of contractions is typical to the I phase of the basic electrical rhythm (BER). Also, retrograde entrainment of duodenal rhythm took place. After 6 day L-NNA injections, GMA was the same as the period between II and III phase of BER. Late second and early third phases predominated, while the I phase wasn’t detected during the recording. In case of long-lasting disorder of NO-system, motor index value significantly differed from the control group samples and depended on the duration of NO-synthase blocking. On the 6th day of L-NNA treatment, the level of motor index increased 1.5 times. GMA phases could be identified only on the basis of motor index values. Stomach’s own rhythms disappeared and duodenogastric reflux resulted in domination of duodenal rhythms. After 12 day L-NNA injections, duration of the II and III phases increased while the I phase of gastric BER disappeared; gastric motor index decreased by 27%. After considering the results of the current investigation, it can be stated that NO system imbalance leads to desynchronization of gastric active phases and, perhaps, reassigns the influence of different compensatory-adaptive mechanisms. The longer is the L-NNA treatment, the more gastric functions are imbalanced and the stronger is the process of destruction.

Identification of a selective inhibitor of murine intestinal alkaline phosphatase (ML260) by concurrent ultra-high throughput screening against human and mouse isozymes

Alkaline phosphatase (AP) isozymes are present in a wide range of species from bacteria to man and are capable of dephosphorylation and transphosphorylation of a wide spectrum of substrates in vitro. In humans, four AP isozymes have been identified—one tissue-nonspecific (TNAP) and three tissue-specific—named according to the tissue of their predominant expression: intestinal (IAP), placental (PLAP) and germ cell (GCAP) APs. Modulation of activity of the different AP isozymes may have therapeutic implications in distinct diseases and cellular processes. For instance, changes in the level of IAP activity can affect gut mucosa tolerance to microbial invasion due to the ability of IAP to detoxify bacterial endotoxins, alter the absorption of fatty acids and affect ectopurinergic regulation of duodenal bicarbonate secretion. To identify isozyme selective modulators of the human and mouse IAPs, we developed a series of murine duodenal IAP (Akp3-encoded dIAP isozyme), human IAP (hIAP), PLAP, and TNAP assays. High throughput screening and subsequent SAR efforts generated a potent inhibitor of dIAP, ML260, with specificity for the Akp3-, compared to the Akp5- and Akp6-encoded mouse isozymes.

Molecular transport machinery involved in orchestrating luminal acid‐induced duodenal bicarbonate secretion in vivo

The duodenal villus brush border membrane expresses several ion transporters and/or channels, including the solute carrier 26 anion transporters Slc26a3 (DRA) and Slc26a6 (PAT-1), the Na(+)/H(+) exchanger isoform 3 (NHE3), as well as the anion channels cystic fibrosis transmembrane conductance regulator (CFTR) and Slc26a9. Using genetically engineered mouse models lacking Scl26a3, Slc26a6, Slc26a9 or Slc9a3 (NHE3), the study was carried out to assess the role of these transporters in mediating the protective duodenal bicarbonate secretory response (DBS-R) to luminal acid; and to compare it to their role in DBS-R elicited by the adenylyl cyclase agonist forskolin. While basal DBS was reduced in the absence of any of the three Slc26 isoforms, the DBS-R to forskolin was not altered. In contrast, the DBS-R to a 5 min exposure to luminal acid (pH 2.5) was strongly reduced in the absence of Slc26a3 or Slc26a9, but not Slc26a6. CFTR inhibitor [CFTR(Inh)-172] reduced the first phase of the acid-induced DBS-R, while NHE3 inhibition (or knockout) abolished the sustained phase of the DBS-R. Luminal acid exposure resulted in the activation of multiple intracellular signalling pathways, including SPAK, AKT and p38 phosphorylation. It induced a biphasic trafficking of NHE3, first rapidly into the brush border membrane, followed by endocytosis in the later stage. We conclude that the long-lasting DBS-R to luminal acid exposure activates multiple duodenocyte signalling pathways and involves changes in trafficking and/or activity of CFTR, Slc26 isoforms Slc26a3 and Slc26a9, and NHE3.

37 Luminal Acid-Associated Post-Prandial Epithelial Hypoxia Maintains the Expression of Iron Absorptive DMT1 and DCYTB, and Cyclooxygenases

Background: We recently identified Slc26a9 as an anion conductance that is upregulated in airway inflammation and prevents bronchial mucus obstruction (Anagnostopoulou et al. JCI 2012). Slc26a9 variants were recently found associated with meconium ileus in cystic fibrosis infants (Sun et al. Nature 2012). Aim: The association with meconium ileus raises the question where Slc26a9 is expressed in the gastrointestinal tract and what is its function. Methods: Acid, HCO3, short circuit current (Isc) measurements were performed in isolated mucosa and acid, HCO3 , and fluid absorptive and secretory rates were measured by single pass perfusion and back titration in anesthetized Slc26a9 KO and WT mice by inhalation of 2.0% isoflurane. Slc26a9 cellular expression was studied by laser dissection and qPCR, and quantitative morphometry was performed in the different segments of the murine gastrointestinal tract. Results: Slc26a9 was found highly expressed in the mucosae of the upper gastrointestinal tract, with abrupt decrease of expression levels to virtually undectable levels beyond the duodenum. As previously reported, Slc26a9 KO mice had completely lost the ability to secrete acid in adulthood. However, Slc26a9 was found highly expressed along the whole gastric gland, even in areas without H+,K+-ATPase expression. Proximal duodenal bicarbonate and fluid secretory rates, which are higher in the proximal than the distal duodenum in WT mice, as well as the ability to stimulate these rates with forskolin, were reduced in the absence of Slc26a9 expression. The gastric antrum, as well as the fundus (after omeprazole treatment to rule out any residual acid secretory capacity) was studied to test whether Slc26a9 transports HCO3 itself. Gastric antrum, while expressing high Slc26a9 levels in WT mice, had lower basal and forskolin-stimulated HCO3 rate as well as lower Isc response in WT than KO mice, arguing against a role of Slc26a9 as a HCO3 transporter. Morphometry revealed strongly elongated fundic as well as antral glands, and slightly elongated proximal duodenal villi as well as crypts. Conclusions: Slc26a9 expression is necessary for normal gastric acid and proximal duodenal bicarbonate secretion, but it is not expressed inmore distal parts of the gastrointestinal mucosa. The increased risk for meconium ileus may be due to loss of digestive function of the stomach and proximal duodenum.

36 Expression and Function of Slc26a9 Member of the SLC26 Anion Transporter Family in the Gastrointestinal Tract

Background: We recently identified Slc26a9 as an anion conductance that is upregulated in airway inflammation and prevents bronchial mucus obstruction (Anagnostopoulou et al. JCI 2012). Slc26a9 variants were recently found associated with meconium ileus in cystic fibrosis infants (Sun et al. Nature 2012). Aim: The association with meconium ileus raises the question where Slc26a9 is expressed in the gastrointestinal tract and what is its function. Methods: Acid, HCO3, short circuit current (Isc) measurements were performed in isolated mucosa and acid, HCO3 , and fluid absorptive and secretory rates were measured by single pass perfusion and back titration in anesthetized Slc26a9 KO and WT mice by inhalation of 2.0% isoflurane. Slc26a9 cellular expression was studied by laser dissection and qPCR, and quantitative morphometry was performed in the different segments of the murine gastrointestinal tract. Results: Slc26a9 was found highly expressed in the mucosae of the upper gastrointestinal tract, with abrupt decrease of expression levels to virtually undectable levels beyond the duodenum. As previously reported, Slc26a9 KO mice had completely lost the ability to secrete acid in adulthood. However, Slc26a9 was found highly expressed along the whole gastric gland, even in areas without H+,K+-ATPase expression. Proximal duodenal bicarbonate and fluid secretory rates, which are higher in the proximal than the distal duodenum in WT mice, as well as the ability to stimulate these rates with forskolin, were reduced in the absence of Slc26a9 expression. The gastric antrum, as well as the fundus (after omeprazole treatment to rule out any residual acid secretory capacity) was studied to test whether Slc26a9 transports HCO3 itself. Gastric antrum, while expressing high Slc26a9 levels in WT mice, had lower basal and forskolin-stimulated HCO3 rate as well as lower Isc response in WT than KO mice, arguing against a role of Slc26a9 as a HCO3 transporter. Morphometry revealed strongly elongated fundic as well as antral glands, and slightly elongated proximal duodenal villi as well as crypts. Conclusions: Slc26a9 expression is necessary for normal gastric acid and proximal duodenal bicarbonate secretion, but it is not expressed inmore distal parts of the gastrointestinal mucosa. The increased risk for meconium ileus may be due to loss of digestive function of the stomach and proximal duodenum.

40 Natural History of Inflammatory Bowel Disease After Liver Transplantation for Primary Sclerosing Cholangitis

Background: We recently identified Slc26a9 as an anion conductance that is upregulated in airway inflammation and prevents bronchial mucus obstruction (Anagnostopoulou et al. JCI 2012). Slc26a9 variants were recently found associated with meconium ileus in cystic fibrosis infants (Sun et al. Nature 2012). Aim: The association with meconium ileus raises the question where Slc26a9 is expressed in the gastrointestinal tract and what is its function. Methods: Acid, HCO3, short circuit current (Isc) measurements were performed in isolated mucosa and acid, HCO3 , and fluid absorptive and secretory rates were measured by single pass perfusion and back titration in anesthetized Slc26a9 KO and WT mice by inhalation of 2.0% isoflurane. Slc26a9 cellular expression was studied by laser dissection and qPCR, and quantitative morphometry was performed in the different segments of the murine gastrointestinal tract. Results: Slc26a9 was found highly expressed in the mucosae of the upper gastrointestinal tract, with abrupt decrease of expression levels to virtually undectable levels beyond the duodenum. As previously reported, Slc26a9 KO mice had completely lost the ability to secrete acid in adulthood. However, Slc26a9 was found highly expressed along the whole gastric gland, even in areas without H+,K+-ATPase expression. Proximal duodenal bicarbonate and fluid secretory rates, which are higher in the proximal than the distal duodenum in WT mice, as well as the ability to stimulate these rates with forskolin, were reduced in the absence of Slc26a9 expression. The gastric antrum, as well as the fundus (after omeprazole treatment to rule out any residual acid secretory capacity) was studied to test whether Slc26a9 transports HCO3 itself. Gastric antrum, while expressing high Slc26a9 levels in WT mice, had lower basal and forskolin-stimulated HCO3 rate as well as lower Isc response in WT than KO mice, arguing against a role of Slc26a9 as a HCO3 transporter. Morphometry revealed strongly elongated fundic as well as antral glands, and slightly elongated proximal duodenal villi as well as crypts. Conclusions: Slc26a9 expression is necessary for normal gastric acid and proximal duodenal bicarbonate secretion, but it is not expressed inmore distal parts of the gastrointestinal mucosa. The increased risk for meconium ileus may be due to loss of digestive function of the stomach and proximal duodenum.

Cystic fibrosis, gastroduodenal inflammation, duodenal ulcer, and H. pylori infection: The “cystic fibrosis paradox” revisited

In cystic fibrosis (CF) patients a duodenal impaired bicarbonate secretion and unbuffered gastric acid are always described and the development of duodenal ulceration is uncommon (CF paradox). Helicobacter pylori (HP) infection is the main cause for duodenal ulceration and its prevalence in CF patients is controversial. The objective of this study is to evaluate HP prevalence, gastric histology, and duodenal ulceration in adult FC patients. 32 adult CF patients were submitted to (13)C-urea breath test and serum immunoblotting test for HP diagnosis. Among them, 20 patients were submitted to endoscopy. 19/32 (68%) patients showed positive serology. Endoscopy showed erosive duodenitis (15%), and duodenal ulcer scar in 10%. On duodenal histology, 94.5%, showed active inflammation and 66.7% gastric metaplasia. HP infection prevalence in adult CF patients was similar to that of general Brazilian population. CF patients have all the duodenal spectrum of alterations, including duodenal ulcer. CF paradox may not exist.

Melatonin decreases duodenal epithelial paracellular permeability via a nicotinic receptor–dependent pathway in rats in vivo

Intestinal epithelial intercellular tight junctions (TJs) provide a rate-limiting barrier restricting passive transepithelial movement of solutes. TJs are highly dynamic areas, and their permeability is changed in response to various stimuli. Defects in the intestinal epithelial TJ barrier may contribute to intestinal inflammation or leaky gut. The gastrointestinal tract may be the largest extrapineal source of endogenous melatonin. Melatonin released from the duodenal mucosa is a potent stimulant of duodenal mucosal bicarbonate secretion (DBS). The aim of this study was to elucidate the role of melatonin in regulating duodenal mucosal barrier functions, including mucosal permeability, DBS, net fluid flux, and duodenal motor activity, in the living animal. Rats were anesthetized with thiobarbiturate, and a ~30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ. Melatonin and the selective melatonin receptor antagonist luzindole were perfused luminally or given intravenously. Effects on permeability (blood-to-lumen clearance of (51)Cr-EDTA), DBS, mucosal net fluid flux, and duodenal motility were monitored. Luminal melatonin caused a rapid decrease in paracellular permeability and an increase in DBS, but had no effect on duodenal motor activity or net fluid flux. Luzindole did not influence any of the basal parameters studied, but significantly inhibited the effects of melatonin. The nonselective and noncompetitive nicotinic acetylcholine receptor antagonist mecamylamine abolished the effect of melatonin on duodenal permeability and reduced that on DBS. In conclusion, these findings provide evidence that melatonin significantly decreases duodenal mucosal paracellular permeability and increases DBS. The data support the important role of melatonin in the neurohumoral regulation of duodenal mucosal barrier.

The electroneutral Na+:HCO3− cotransporter NBCn1 is a major pHi regulator in murine duodenum

Duodenocyte pHi control and HCO3 − secretion protects the proximal duodenum against damage by gastric acid. The molecular details of duodenocyte pH control are not well understood. A selective duodenal expression (within the upper GI tract) has been reported for the electroneutral Na+:HCO3 − cotransporter NBCn1 (Slc4a7). We aimed to determine the role of NBCn1 and NBCe2 in duodenocyte intracellular pH regulation as well as basal and agonist-stimulated duodenal bicarbonate secretion (JHCO3 −), exploiting mouse models of genetic slc4a7 and slc4a5 disruption. Basal and forskolin (FSK)-stimulated JHCO3 − was measured by single-pass perfusion in the duodenum of slc4a7−/− and slc4a7+/+ as well as slc4a5−/− and slc4a5+/+ mice in vivo, and by pH-stat titration in isolated duodenal mucosa in vitro. Duodenocyte HCO3 − uptake rates were fluorometrically assessed after acidification of intact villi and of isolated duodenocytes. Slc4a7−/− mice displayed significantly lower basal and FSK-stimulated duodenal HCO3 − secretion than slc4a7+/+ littermates in vivo. FSK-stimulated HCO3 − secretion was significantly reduced in slc4a7−/− isolated duodenal mucosa. Na+- and HCO3 −-dependent base uptake rates were significantly decreased in slc4a7−/− compared with slc4a7+/+ villus duodenocytes when measured in intact villi. Carbonic anhydrase (CA)-mediated CO2 hydration played no apparent role as a HCO3 − supply mechanism for basal or FSK-stimulated secretion in the slc4a7+/+ duodenum, but was an important alternative HCO3 − supply mechanism in the slc4a7−/− duodenum. NBCe2 (Slc4a5) displayed markedly lower duodenal mRNA expression levels, and its disruption did not interfere with duodenal HCO3 − secretion. The electroneutral Na+:HCO3 − cotransporter NBCn1 (slc4a7) is a major duodenal HCO3 − importer that supplies HCO3 − during basal and FSK-stimulated HCO3 − secretion.

Endoscopic pancreatic function test using combined secretin and cholecystokinin stimulation for the evaluation of chronic pancreatitis

Current endoscopic pancreatic function test (ePFT) methods use either secretin or cholecystokinin (CCK) to measure pancreatic function. To evaluate a novel ePFT protocol that includes both secretin and CCK stimulation and to assess which fluid parameters best discriminate patients with chronic pancreatitis (CP). Prospective, cross-sectional diagnostic study. Single, tertiary-care institution. Healthy volunteers and patients evaluated for CP were included. All patients underwent a combined secretin-CCK ePFT. Patients evaluated for CP also underwent EUS during the same endoscopic session. Duodenal fluid bicarbonate, lipase, and amylase concentrations were measured after CCK and secretin stimulation. Results were compared based on the presence of CP detected by EUS (≥5 features). Twenty healthy volunteers and 69 patients evaluated for CP completed the secretin and CCK ePFT. Patients with an EUS score of 5 or higher had significantly decreased peak bicarbonate concentrations (72 mmol) compared with patients with an EUS score lower than 5 (90 mmol) and healthy subjects (108 mmol) (P < .001). Peak concentrations of amylase and lipase and total fluid volume were not significantly different between patients with CP and controls. Receiver-operating characteristic analysis revealed that peak bicarbonate concentration had superior discrimination for CP (area under the curve [AUC] 0.738) compared with peak amylase (AUC 0.677) and peak lipase (AUC 0.627). The addition of enzyme concentration measurement did not improve discrimination compared with peak bicarbonate alone. Secretin and cholecystokinin endoscopic pancreatic function test (SC ePFT) results were not compared with those of single hormone ePFTs. The addition of CCK infusion and enzyme concentration measurement to a standard secretin ePFT does not enhance the diagnosis of CP.

Neuronal cGMP kinase I is essential for stimulation of duodenal bicarbonate secretion by luminal acid

Brief contact of the duodenal mucosa with luminal acid elicits a long-lasting bicarbonate (HCO(3)(-)) secretory response, which is believed to be the primary protective mechanism against mucosal damage. Here, we show that cGMP-dependent protein kinase type I-knockout (cGKI(-/-)) mice are unable to respond to a physiological H(+) stimulus with a HCO(3)(-) secretory response and spontaneously develop duodenal ulcerations. Smooth muscle-selective cGKI knock-in rescued the motility disturbance but not the defective HCO(3)(-) secretion. Proton-induced HCO(3)(-) secretion was not attenuated by selective inactivation of the cGKI gene in interstitial cells of Cajal or in enterocytes, but was abolished by inactivation of cGKI in neurons (ncGKI(-/-)). cGKI was expressed in the brainstem nucleus tractus solitarius that connects the afferent with the efferent N. vagus. Accordingly, truncation of the subdiaphragmal N. vagus significantly diminished proton-induced HCO(3)(-) secretion in wild-type mice, whereas stimulation of the subdiaphragmal N. vagus elicited a similar HCO(3)(-) secretory response in cGKI(-/-), ncGKI(-/-) and wild-type mice. These findings show that protection of the duodenum from acid injury requires neuronal cGKI.

Umami Receptor Activation Increases Duodenal Bicarbonate Secretion via Glucagon-Like Peptide-2 Release in Rats

Luminal nutrient chemosensing during meal ingestion is mediated by intestinal endocrine cells, which regulate secretion and motility via the release of gut hormones. We have reported that luminal coperfusion of L-Glu and IMP, common condiments providing the umami or proteinaceous taste, synergistically increases duodenal bicarbonate secretion (DBS) possibly via taste receptor heterodimers, taste receptor type 1, member 1 (T1R1)/R3. We hypothesized that glucose-dependent insulinotropic peptide (GIP) or glucagon-like peptide (GLP) is released by duodenal perfusion with L-Glu/IMP. We measured DBS with pH and CO(2) electrodes through a perfused rat duodenal loop in vivo. GIP, exendin (Ex)-4 (GLP-1 receptor agonist), or GLP-2 was intravenously infused (0.01-1 nmol/kg/h). l-Glu (10 mM) and IMP (0.1 mM) were luminally perfused with or without bolus intravenous injection (3 or 30 nmol/kg) of the receptor antagonists Pro(3)GIP, Ex-3(9-39), or GLP-2(3-33). GIP or GLP-2 infusion dose-dependently increased DBS, whereas Ex-4 infusion gradually decreased DBS. Luminal perfusion of l-Glu/IMP increased DBS, with no effect of Pro(3)GIP or Ex-3(9-39), whereas GLP-2(3-33) inhibited L-Glu/IMP-induced DBS. Vasoactive intestinal peptide (VIP)(6-28) intravenously or N(G)-nitro-L-arginine methyl ester coperfusion inhibited the effect of L-Glu/IMP. Perfusion of L-Glu/IMP increased portal venous concentrations of GLP-2, followed by a delayed increase of GLP-1, with no effect on GIP release. GLP-1/2 and T1R1/R3 were expressed in duodenal endocrine-like cells. These results suggest that luminal L-Glu/IMP-induced DBS is mediated via GLP-2 release and receptor activation followed by VIP and nitric oxide release. Because GLP-1 is insulinotropic and GLP-2 is intestinotrophic, umami receptor activation may have additional benefits in glucose metabolism and duodenal mucosal protection and regeneration.

The role of cGMP-cGKI-signaling for duodenal bicarbonate secretion

Results Gastric acid production was similar in control and mutant mice. The basal secretion rate of bicarbonate was strongly reduced in the different gene-targeted cGKI mice. Protons induced bicarbonate secretion in controls but not in mutant mice. The dysfunction of the duodenal bicarbonate secretion of RM and cGKI-KO animals was associated with severe gastrointestinal bleedings, which were caused by the age-dependent aggravation of an epithelial ulceration that localized to the papilla Vateri. In conclusion, the analysis of cGKI-KO and RM indicates that a cGMP-cGKI-dependent pathway is present in non-smooth muscle cells of the duodenum, that is involved in the basal and acid-induced secretion of bicarbonate. We suppose, that cGKI might be expressed in the enteric nervous system. Furthermore we hypothesize a crucial role for cGKI signaling via the N. vagus. In contrast to the widespread assumption, that cGKI is expressed in duodenal cells of Cajal we were not able to detect any cGKI in these cells. Conclusion The inability to secrete adequate amounts of bicarbonate ultimately leads to duodenal ulceration. We postulate that the continuous blood loss accounts for the chronic anemia of cGKI mutant mice and causes the premature death of the cGKI-KOs and RM. To administer a therapy against the ulceration and their effects, cGKI knockout mice were treated with a proton pump inhibitor. Chronical treatment of conventional cGKI knockout mice with the proton pump inhibitor esomeprazol prolonged their life expectancy significantly in contrast to the untreated cGKI-knockout mice.

Estrogen Regulation of Duodenal Bicarbonate Secretion and Sex-Specific Protection of Human Duodenum

The reason that women have a lower prevalence of duodenal ulcer is not clear. We investigated whether estrogen regulates human duodenal bicarbonate secretion (DBS) and whether this process accounts for sex differences in the prevalence of duodenal ulcer. We performed an epidemiologic study to correlate duodenal ulcer prevalence with sex and age. Proximal DBS was measured from healthy subjects. Estrogen-receptor expression was examined in human duodenal mucosa by immunoblot and immunohistochemical analyses. Among women, the prevalence of duodenal ulcer was significantly lower than among men. The reduced prevalence was greatest among premenopausal women (20-49 y), who were 3.91- to 5.09-fold less likely to develop duodenal ulcers than age-matched men; the difference was reduced to 1.32-fold or less among subjects aged 60 years or older. Premenopausal (20-29 y), but not postmenopausal (60-69 y), women had significantly higher basal and acid-stimulated DBS than the age-matched men. Basal and acid-stimulated DBS in premenopausal women (20-29 y) were significantly higher than in postmenopausal women (60-69 y), whereas there were no significant differences in basal or acid-stimulated DBS between men who were aged 20-29 years or 60-69 years. Serum levels of estradiol changed in parallel with basal and acid-stimulated DBS during the physiological menstrual cycle in premenopausal women. 17β-estradiol-stimulated DBS was independent of age or sex. Estrogen receptors α and β were detected on plasma membranes and in the cytosol of human duodenal epithelial cells. Estrogen regulates human DBS, which could reduce the risk for duodenal ulcer in women and contribute to sex differences in the prevalence of duodenal ulcer.

Dipeptidyl peptidase IV inhibitor potentiates duodenal bicarbonate secretion and prevents intestinal mucosal injury in rats

Luminal nutrients stimulate enteroendocrine cells, which release gut hormones, including glucagon-like peptide-2 (GLP-2). Luminal co-perfusion of L-glutamate (L-Glu) and 5′-inosine monophosphate (IMP) synergistically increases duodenal bicarbonate secretion (DBS) via GLP-2 release, rapidly degraded by dipeptidyl peptidase (DPP) IV. We thus hypothesized that DPPIV inhibition enhances luminal nutrient-induced DBS and prevents intestinal injury. We measured DBS in a perfused rat duodenal loop. L-Glu and IMP were co-perfused +/− perfusion or iv injection of a selective DPPIV inhibitor NVP-728. The effect of a long-acting DPPIV inhibitor K579 (ig or ip) was also examined on indomethacin (IND)-induced intestinal injury. DPPIV activity was highly present on the brush border and submucosal layer. L-Glu/IMP perfusion increased DBS, inhibited by the GLP-2 receptor antagonist. NVP-728 iv enhanced the L-Glu/IMP-induced DBS, whereas perfused NVP-728 had no effect, suggesting that submucosal DPPIV degrades GLP-2. Pretreatment of K579 dose-dependently reduced the index of IND-induced intestinal ulcers. DPPIV inhibition potentiated L-Glu/IMP-induced DBS via GLP-2 pathway and prevented intestinal injury, suggesting that the modulation of endogenous GLP-2 by luminal nutrients and DPPIV inhibition may be therapeutic for intestinal mucosal injury and healing. Ajinomoto Inc, R01 DK54221

Luminal ATP release is enhanced in multidrug resistant protein Mdr1a knockout mouse duodenum

Extracellular ATP release is an essential component of the luminal purinergic system, which along with P2Y receptors and alkaline phosphatase (AP) helps regulate duodenal bicarbonate secretion (DBS). Since ATP release is reduced by CFTR inhibition or genetic deletion of murine intestinal AP (with downregulation of the multidrug resistant proteins Mdr1a and Mrp2), we hypothesized that Mdr1a knockout (KO) decreases ATP release. We measured DBS and ATP output in a perfused duodenal loop in male wild type (WT) or MDR1a KO mice, or in rats. The duodenal loop was perfused with the competitive AP substrate glycerol phosphate (GP) with or without the P2 receptor antagonist/ENTPDase inhibitor suramin, the MRP inhibitor MK571 or pannexin (Panx) inhibitor. AP inhibition with GP increased DBS and non-lytic ATP output in WT mouse and rat duodena. Co-perfusion of suramin inhibited GP-induced DBS, but enhanced ATP output. In KO duodenum, GP or suramin enhanced ATP output without parallel LDH release, inhibited by CFTRinh-172. Expression of Panx1 and MRP1 was selectively upregulated in KO duodenum. Luminal perfusion of MK571 or Panx inhibitor reduced GP-induced ATP release in rat duodenum. MDR1a, CFTR and Panx1 may coordinately contribute to duodenal epithelial ATP release. Enhanced ATP release may account for the induction of diarrhea followed by colitis as part of the Mdr1a KO intestinal phenotype. NIH-NIDDK R01 DK54221

Estrogen Might Protect Against Duodenal Ulcers

Studies have shown that women are less likely than men to develop duodenal ulcers (DUs). Other studies have suggested that estrogen stimulates duodenal bicarbonate secretion, which could be a biological mechanism for the lower incidence of DUs among women. To investigate this possible link, researchers in China conducted an epidemiologic study involving 64,385 patients who underwent endoscopy for dyspepsia. …

Duodenal epithelial sensing of luminal acid: role of carbonic anhydrases

Sensing the luminal contents is a prerequisite to activate appropriate gastrointestinal functions. A major task of the duodenal epithelium is to resist the repeated challenges of hydrochloric acid expelled from the stomach. Although extensive research in this field, the complete mechanisms providing this defence remain to be revealed. The duodenal epithelium exports bicarbonate into a submillimetre-thick mucus gel on top of the mucosal surface. Despite the very low pH of the luminal contents, the duodenal mucus-bicarbonate barrier provides a means of maintaining a virtually neutral pH at the epithelial surface. Instead of pH, CO₂ generated by the mixing of acid and bicarbonate at levels not found elsewhere in the body serves as the mediator for sensing the luminal acid. Carbonic anhydrases (CAs) catalyse the reversible hydration of CO₂ and are heavily expressed in the duodenal segment. Accumulating data support the key function of CAs in sensing luminal acid and CO₂. Recent advances demonstrate that the presence of CA II in upper villus plays a crucial role in enterocyte intracellular acidification preceding the secretory increase in response to luminal acid. However, CAs only have a minor role in the bicarbonate supply destined for duodenal bicarbonate secretion into the lumen. The purpose of this review is to summarize the current knowledge of how intraluminal acid is sensed by the duodenal mucosa, with a focus on the role of CAs.

Expression of acid‐sensing ion channels in intestinal epithelial cells and their role in the regulation of duodenal mucosal bicarbonate secretion

As little is currently known about acid-sensing ion channels (ASICs) in intestinal epithelial cells, the aims of the present study were to investigate the expression and function of ASICs in intestinal epithelial cells, particularly their physiological role in the acid-stimulated duodenal mucosal bicarbonate secretion (DMBS). RT-PCR and digital Ca²(+) imaging were used to determine the expression and function of ASICs in HT29 cells and SCBN cells, intestinal epithelial crypt cell lines. The acid-stimulated DMBS was measured in C57 black mice in vivo to study the role of ASICs in this physiological process. ASIC1a mRNA expression was detected in the duodenal mucosa stripped from mice and epithelial cell lines, in which cytoplasmic free Ca²(+) ([Ca²(+) ](cyt)) in response to extracellular acidosis was also increased. In Ca²(+) -containing solutions, acidosis (pH 6.0-5.0) raised [Ca²(+) ](cyt) in both HT29 cells and SCBN cells in a similar pH-dependent manner. Acidosis-induced increase in [Ca²(+) ](cyt) was markedly inhibited by amiloride (an ASICs blocker), SK&F96365 (a blocker for non-selective cation channels), or in Ca²(+) -free solutions; but was abolished by amiloride in Ca²(+) -free solutions. However, acidosis-induced increase in [Ca²(+) ](cyt) was slightly affected by U73122 (a PLC inhibitor), or nifedipine (a voltage-gated Ca²(+) channel blocker). After acidosis raised [Ca²(+) ](cyt) , stimulation of purinergic receptors with ATP further increased [Ca²(+) ](cyt) , but acidosis-induced increase in [Ca²(+) ](cyt) was not altered by suramin. Moreover, acid-stimulated murine DMBS was significantly attenuated by amiloride. Therefore, ASICs are functionally expressed in intestinal epithelial cells, and may play a role in acid-stimulated DMBS through a Ca²(+) signalling pathway.

Fecal Elastase: A Useful Test for Pancreatic Insufficiency?

This is an excerpt from the content: Pancreatic fecal elastase-1 (FE-1) has become the first-line test of pancreatic function. Our experience as a referral center for pancreatic disease suggests that in the minds of most gastroenterologists, a low FE-1 is diagnostic of pancreatic insufficiency. The paper by Evans and colleagues in the current issue of this journal highlights some weaknesses of that assumption in patients with Celiac disease. FE-1, first described by Balo and Banga in 1950 [1], is one of a family of protease enzymes secreted by acinar cells. FE-1 is well documented in quantitative studies to be stable during intestinal transit and studies demonstrate significant correlation between fecal elastase and levels of other pancreatic enzymes such as duodenal lipase, amylase, trypsin, and bicarbonate concentration [2–6]. Fecal elastase is concentrated in human feces compared with pancreatic juice and is a simple, non-invasive and inexpensive test [2, 7, 8]. As a result, FE-1 has replaced “tube tests” and fecal fat ...