Duodenal Secretion Research Articles

Diagnosing Pancreatic Cancer Using Methylation Specific PCR Analysis

The aim of this study was to determine the utility of detecting methylated ppENK and p16 in pancreatic juice by methylation specific PCR as a marker of pancreatic adenocarcinoma. Pancreatic juice samples were collected either intraoperatively, from 92 patients undergoing pancreaticoduodenectomy for benign (n = 20) and malignant periampullary disease (n = 72) or endoscopically (by duodenal aspiration after secretin infusion), from 13 patients undergoing investigation for pancreatic disease. Methylated ppENK was detected in the pancreatic juice of 30 (66.7%) of 45 patients with pancreatic ductal adenocarcinoma, in 4 (44.4%) of 9 patients with intraductal papillary-mucinous adenocarcinoma, and in 7 (41.2%) of 17 patients with other periampullary carcinomas, using methylation specific PCR. Methylated p16 was detected in a lower percentage of these patients (11.1%, 11.1% and 23.5%, respectively). In contrast, methylated ppENK and p16 were not detected in 21 patients with non-malignant disease including 12 patients with chronic pancreatitis. Methylated ppENK was detected in 30 of 33 (90.9%) primary pancreatic adenocarcinoma and methylated p16 was in 6/33 (18.2%). Despite the absence of ppENK and p16 methylation in normal pancreas, methylated ppENK and p16 was present in the duodenum of 90.5% and 28.6%, respectively of patients without cancer. Further, methylated ppENK and p16 was seen in 88.9% and 11.1%, respectively of pancreatic juice samples obtained by duodenal aspiration from patients without cancer. We conclude that since ppENK and p16 are not normally methylated in pancreatic secretions, detection of methylated ppENK and p16 in pure pancreatic juice obtained by direct cannulation of the pancreatic duct to avoid duodenal secretions may suggest the presence of pancreatic adenocarcinoma Key Words: Pancreatic juice, Methylation, ppENK, Pancreatic adenocarcinoma

Duodenal defence mechanisms: role of mucosal bicarbonate secretion

The duodenal epithelium secretes bicarbonate at higher rates than does the stomach (or more distal small intestine) and the duodenal secretion is currently accepted as the most important defence mechanism against acid discharged from the stomach. HCO3- entering the continuous layer of visco-elastic mucus gel on top of the epithelial surface maintains pH in its cell-facing portion at neutrality at acidities encountered in the healthy duodenum. The secretion is decreased in patients with acute and chronic duodenal ulcer disease and is inhibited by non-steroidal anti-inflammatory agents. Studies of the neurohumoral control of the duodenal alkaline secretion and of acid/base transport processes and intracellular signaling in duodenal enterocytes are currently of great research interest.

COX inhibition excites enteric nerves that affect motility, alkaline secretion, and permeability in rat duodenum.

In anesthetized rats, the cyclooxygenase (COX) inhibitor indomethacin induces duodenal motility, increases duodenal mucosal alkaline secretion (DMAS), and evokes a transient increase in duodenal paracellular permeability (DPP). To examine whether enteric nerves influence these responses, the duodenum was perfused with lidocaine. Motility was assessed by measuring intraluminal pressure, and DPP was determined as blood-to-lumen clearance of (51)Cr-EDTA. DMAS was assessed by titration. In control animals, few contractions occurred during saline perfusion and lidocaine did not alter this condition. Perfusion with 0.03-0.1% lidocaine did not affect DMAS or DPP whereas 0.3-1% lidocaine reduced DMAS and increased DPP. Indomethacin induced motility and doubled DMAS. Application of 0.03% lidocaine on the duodenal serosa reduced motility and DMAS whereas 0.03% lidocaine applied luminally inhibited DMAS only. Higher concentrations of lidocaine abolished the increase in DMAS and changed the motility pattern to numerous low-amplitude contractions, the latter effect being blocked by iloprost. The lidocaine-induced increases in DPP were markedly higher than in controls. We conclude that indomethacin activates enteric nerves that induce motility, increase DMAS, and decrease DPP.

Stereologic description of the changing expression of constitutive nitric oxide synthase and heme oxygenase in the enteric plexuses of the pig small intestine during development.

The similarities between heme oxygenase-2 (HO-2) and nitric oxide synthase (nNOS) and the transient expression of nNOS during development led us to investigate whether both systems are similarly affected by changes that occur during development and by regional differences along the small intestine. By combining NADPH diaphorase histochemistry and HO-2 immunohistochemistry on whole-mount preparations and by using stereologic methods, a qualitative and quantitative description of HO-2 and nNOS expression was obtained. Examinations were carried out on the small intestine of fetal, 1-2-day and 5-6-week-old pigs. In all age groups, three enteric plexuses were distinguished. The presence of HO-2-immunoreactive (HO-2-IR) and NADPH diaphorase-positive neurons corresponded to earlier morphological and physiological reports. Nevertheless, the total number of nitrergic neurons remained constant or decreased in the enteric plexuses, whereas the total number of HO-2-IR neurons displayed an overall increase. Changing concentrations of glucocorticoids, target-derived signals, presynaptic input, and an effect of HO-2 activity on nNOS synthesis are likely to play roles in the observed developmental changes. The numerical density of HO-2-IR neurons remained relatively constant along the intestinal tract; in contrast, the nitrergic neurons were most numerous in the inner submucous and myenteric plexus in the duodenum and ileum, respectively. It is believed that the duodenal nitrergic neurons in the inner submucous plexus could be involved in the regulation of duodenal secretion processes, whereas the region-dependent density in the myenteric plexus possibly forms the morphological basis for a regionally different participation of NO in the relaxation of the small intestine.

Angiotensin II type 2 receptor-mediated duodenal mucosal alkaline secretion in the rat.

The aims of this study were to elucidate the distribution of angiotensin receptors (AT(1) and AT(2)) in the duodenal wall and to investigate whether AT(2) receptors are involved in the regulation of duodenal mucosal alkaline secretion, which is of importance for the mucosal defense against gastric acid. Immunohistochemistry was used to locate AT(1) and AT(2) receptors in chloralose-anesthetized rats. Duodenal mucosal alkaline output was measured by use of in situ pH-stat titration. Immunohistochemistry demonstrated a distinct staining for both AT(1) and AT(2) receptors in the lamina propria of the villi and also for AT(1) receptors in the muscularis interna. When angiotensin II was infused in the presence of the AT(1) receptor antagonist losartan, mucosal alkaline secretion increased by ~50%. This response was inhibited by the AT(2) receptor antagonist PD-123319. The AT(2) receptor agonist CGP-42112A increased mucosal alkaline secretion by ~50%. This increase was absent in the presence of PD-123319 but not in the presence of losartan or the local anesthetic lidocaine. We conclude that angiotensin II stimulates duodenal mucosal alkaline secretion by activation of AT(2) receptors located in the duodenal mucosa/submucosa.

The Pathogenesis and Diagnosis of Bile Reflux Gastropathy

Bile reflux gastropathy is a disease caused by reflux of duodenal fluid to the gaster. This fluid contains pancreatic juices and duodenal secretion. The manifestations that occur depend on the frequency, amount, and duration of reflux. This disorder is quite rarely recognized in daily clinical practice. Endoscopy of the upper gastrointestinal tract is required to establish the diagnosis of this disorder. This paper will give a brief view of the pathogenesis and diagnostic method for this disorder. Keywords: gastropathy, bile reflux, motility

Dynamic involvement of the inducible type of nitric oxide synthase in acid-induced duodenal mucosal alkaline secretion in the rat.

It has previously been shown that mucosal nitric oxide synthase (NOS) is involved in acid-induced duodenal mucosal alkaline secretion. The primary aim of the present study was to elucidate which isoform of NOS is responsible in rats. Immunohistochemistry showed that inducible NOS (iNOS) was constitutively expressed in villous epithelial cells. Exposing the duodenal mucosa to 10 mM HCl resulted in an increased duodenal mucosal alkaline secretion. This response was totally inhibited by intraluminal administration of a selective inhibitor of iNOS (L-N6-1-iminoethyl-lysine). One hour after the acid exposure, western blot technique showed a marked increase in mucosal iNOS expression. A second acid exposure resulted in a further stimulation of alkaline secretion. These data suggest that exposure of the duodenal mucosa to HCI initiates an increased mucosal alkaline secretion, via NO synthesis mediated by iNOS located in the epithelial cells of the villi. In addition, luminal acid stimulates expression of iNOS.

Gastrointestinal cytoprotection by prostaglandin E and EP receptor subtypes

Endogenous prostaglandins (PGs) play important roles in modulating the mucosal integrity and various functions of the gastrointestinal tract. Among them, E-type PGs are most effective in these actions. This article reviews recent studies dealing with the relationship of the cytoprotective action of PGE2- and EP-receptor subtypes in the gastrointestinal mucosa. PGE2 exerts gastric cytoprotection against HCl/ethanol and indomethacin. These effects were mimicked by only EP1 agonists and attenuated by EP1 antagonists. Likewise, the adaptive cytoprotection induced by a mild irritant was attenuated by EP1 antagonists as well as indomethacin. On the other hand, the protective effect of dmPGE2 against indomethacin-induced small intestinal lesions was mimicked by only EP3 and EP4 agonists. Similar results were obtained in EP-receptor knockout mice; i.e., PGE2 failed to exhibit both direct and adaptive cytoprotection in EP1-receptor knockout mice, while the protective action in both the duodenum and small intestine was hampered in EP3-receptor knockout mice. The underlying mechanism related to these actions of PGE2 in the stomach, duodenum or small intestine may be related to inhibition of stomach contraction, stimulation of duodenal alkaline secretion, or suppression of bacterial translocation due to inhibition of intestinal contraction as well as stimulation of mucus secretion, respectively.

Effects of hypovolaemia on acid-induced duodenal mucosal damage in the rat.

Modest acute hypovolaemia in rats markedly decreases the duodenal mucosal alkaline secretion via neurohumoral links. The present study was undertaken to investigate if such a procedure influences the morphological changes observed following an acid challenge of the duodenal mucosa. Experiments were performed on anaesthetized male Sprague-Dawley rats. HCl (10 or 100 mM) was infused during 15 min into the duodenum via a luminally situated catheter. Time controls were compared with animals bled 10% of total blood volume. Mucosal damage was evaluated by light microscopic morphometry on transverse sections and by scanning electron microscopy of the luminal surface. Perfusion with either 10 mM or 100 mM HCl reduced villus length by about 30%. The villus area was unaffected by 10 mM HCl, but was reduced significantly by 10% by 100 mM HCl as compared with NaCl time controls. Hypovolaemia did not influence the morphometrical changes induced by 10 mM HCl but reduced significantly both villus length (-28%) and villus area (-10%) as compared with the unbled 100 mM HCl group. Scanning electrone microscopy (SEM)-based visual damage score was not influenced by the hypovolaemia procedure in any of the acidities. Morphological changes of the duodenal mucosa, induced by moderate intra-luminal acidity (10 mM HCl), is not influenced by hypovolaemia. However, at higher acidities (100 mM HCl) the hypovolaemia contributes to more severe mucosal damage.

Inhibition of nitric oxide synthesis augments pulmonary oedema in isolated perfused rabbit lung

The role of nitric oxide (NO) in precipitating pulmonary oedema in acute lung injury remains unclear. We have investigated the mechanism of involvement of NO in the maintenance of liquid balance in the isolated rabbit lung. Thirty pairs of lungs were perfused with colloid for up to 6 h, during which pulmonary vascular resistance (PVR) and capillary pressure (PCP) were measured frequently, and time to gain 5 g in weight (t5) was recorded. Four protocols with different perfusate additives were studied: (i) none (control, n = 11); (ii) 10 mmol NG-nitro-L-arginine methyl ester (L-NAME) (n = 6); (iii) 10 mmol L-NAME with 100 mumol lodoxamide, an inhibitor of mast cell degranulation (n = 7); (iv) 10 mmol L-NAME with 10 mumol 8-bromo-3',5'-cyclic guanosine monophosphate (8Br-cGMP), an analogue of cGMP that may reduce vascular permeability by relaxing contractile elements in endothelial cells (n = 6). Neither PVR nor PCP differed between protocols. L-NAME markedly reduced t5 from 248 (27) min (mean (SEM)) in protocol (i) to 144 (5) min in protocol (ii) (P < 0.05). Both lodoxamide (t5 = 178 (7) min) and 8Br-cGMP (t5 = 204 (10) min) substantially corrected the effect of L-NAME (P < 0.005). Results suggest that maintenance of a low permeability by NO may involve mast cell stabilization and endothelial cell relaxation.

Correlations between antibody immune responses at different mucosal effector sites are controlled by antigen type and dosage.

Monitoring specific secretory immunoglobulin A (IgA) responses in the intestines after mucosal immunization or infection is impeded by the fact that sampling of small intestinal secretions requires invasive methods not feasible for routine diagnostics. Since IgA plasma cells generated after intragastric immunization are known to populate remote mucosal sites as well, secretory IgA responses at other mucosal surfaces may correlate to those in the intestines and could serve as proxy measures for IgA secretion in the gut. To evaluate the practicability of this approach, mice were immunized intragastrically with 0.2, 2, and 20 mg of ovalbumin plus 10 microg of cholera toxin, and the antigen-specific local secretory IgA responses in duodenal, ileal, jejunal, rectal, and vaginal secretions, saliva, urine, and feces, as well as serum IgG and IgA responses were analyzed by enzyme-linked immunosorbent assay. Correlation analysis revealed significant relationships between serum IgG and IgA, urinary IgA, salivary IgA, and secretory IgA in duodenal, jejunal, ileal, and rectal secretions for the 0.2-mg but not for the 20-mg ovalbumin dose. Fecal samples were poor predictors for intestinal antiovalbumin IgA responses, and no correlations could be established for cholera toxin, neither between local anti-cholera toxin levels nor to the antiovalbumin responses. Thus, specific IgA in serum, saliva, or urine can serve as a predictor of the release of specific IgA at intestinal surfaces after intragastric immunization, but the lack of correlations for high ovalbumin doses and for cholera toxin indicates a strong dependency on antigen type and dosage for these relationships.

Guanylate cyclase C (GC-C) mediates calcium-activated duodenal mucosal bicarbonate secretion

Activation of GC-C by heat stable toxin of E. coli (STa) acts via cGMP resulting in duodenal Cl and HCO:; secretion (DMBS). It has been proposed that cGMP regulates increases in [Ca We previously demonstrated in GC-C knockout mice that absence of functional GC-C results in decreased DMBS in vitro in response to STa and PGEz (Gastroenterology 1999;116:A890). The purpose of these studies was to determine whether GC-C (likely cGMP) mediates Ca-induced DMBS. Bicarbonate secretion was quantitated in vitro using a murine knockout model (GC-C gene-ablated; GC-C -1-), and the results contrasted to normal littermates (GC-C +J+). The proximal 8 mm of duodenum was resected and the stripped mucosa mounted in Ussing chambers under short-circuited conditions. The mucosal (HCO:;-free) and serosal (HCO;-containing) sides were bathed in modified Ringer's at 37°C. Basal HCO; secretion and Iso were measured for 20 min and then stimulated with either carbachol (10-4M), the calcium ionophore A23187 (10-5M), or thapsigargin (10AM) to increase [Ca [separate tissues (N = 5), additions to the serosal bath]. Compared to GC-C +1+, carbacholand A23187-stimulated DMBS were markedly (P < 0.01) impaired in GC-C -1tissues (Table, *=P <0.01 vs GC-C+I+). In contrast, thapsigargin-induced increases in DMBS were similar in GC-C -1and GC-C +1+ (Table). The I, responses corresponded with DMBS. While release of intracellular Ca'2+ stores by thapsigargin increased DMBS in GC-C -1similar to GC-C +1+ tissues, DMBS remained essentially unchanged when activated by either the receptormediated agonist (carbachol) or Ca2+ influx (A23187). Thus, these findings implicate a GC-C pathway as a key factor in Caz+-activated mammalian duodenal mucosal bicarbonate secretion.

Variability in the composition of physiologic duodenogastric reflux

Duodenogastric reflux has long been associated with various diseases of the foregut. Even though bile is often used as a marker, duodenogastric reflux consists of other components such as pancreatic juice and duodenal secretions. The aim of this study was to investigate the occurrence of duodenogastric reflux, its components, and the variability of its composition in normal subjects. Twenty healthy volunteers (7 men and 13 women) whose median age was 24 years underwent combined 24-hour bilirubin and gastric pH monitoring and intraluminal gastric aspiration. All probes were placed at 5 cm below the lower border of the lower esophageal sphincter. Aspiration was performed hourly and at any time when bilirubin and/or pH monitoring showed signs of duodenogastric reflux. Elastase and amylase were measured in the aspirate. All volunteers had episodes of physiologic duodenogastric reflux. A total of 70 episodes of duodenogastric reflux were registered with a median of three episodes (range 1 to 8) per subject. Most bile reflux occurred separately from pancreatic enzyme reflux. Pancreatic enzyme aspirate was significantly more often associated with a rise in pH in comparison to bile reflux ( P <0.01). Duodenogastric reflux is a physiologic event with varying composition. Both bile and pancreatic enzyme reflux frequently occur separately. These findings could explain the disagreement regarding assessment and interpretation of duodenogastric reflux in the past. Thus monitoring of duodenogastric reflux requires more than the detection of just one component.

Distant intestinal stimulation by cholera toxin in rat in vivo

Cholera toxin (16 μg/rat) locally administered in the jejunum of anesthetized rats stimulated jejunal secretion and also distant duodenal secretion, as determined with the ligated loop technique. The release of prostaglandin E 2 in both jejunal and duodenal secretions and in plasma was increased by cholera toxin, while the release of 5-hydroxytryptamine (5-HT) was unchanged in the early phase of secretion (2 h). The inhibitor of prostaglandin E 2 release, indomethacin (10 mg/kg, s.c.), and the 5-HT 3 subtype receptor antagonist, granisetron (30 μg/kg i.v.), inhibited the jejunal secretion but had no effect on distant duodenal secretion. However, indomethacin statistically significantly decreased prostaglandin E 2 release in both jejunal and duodenal secretions as well as in plasma. The vasoactive intestinal peptide antagonist (VIP-(6–28), 1.2 nmol/100 g h) did not modify jejunal and duodenal secretions. Our study confirmed the local involvement of 5-HT and prostaglandin E 2 in choleraic jejunal secretion but not in distant duodenal secretion.

Utility of endoscopic biopsy samples to quantitate human duodenal ion transport

Duodenal mucosal bicarbonate secretion (DMBS) prevents acid-peptic damage and facilitates nutrient absorption. DMBS is diminished in patients with duodenal ulcers and is normalized after Helicobacter pylori eradication. The measurement of DMBS in human patients in vivo requires intubation with a multi-lumen balloon tube and permits limited testing with putative agonists and antagonists. Our purpose was to develop a means to investigate transport events in human duodenal biopsy samples in vitro. After validation studies in a modified mini-Ussing chamber were performed, duodenal transport events were examined in proximal endoscopic biopsy samples from normal volunteers (n = 17). Tissues were mounted in modified mini-Ussing chambers (volume 2.5 ml, surface area 3.8 mm 2). Short circuit current (I sc), potential difference (PD), and bicarbonate secretion were determined under basal conditions and after stimulation with graded doses of prostaglandin E 2 (PGE 2)(10 −8 to 10 −4 mol/L) and dibutyryl cAMP (db-cAMP)(10 −4 to 10 −2 mol/L). Duodenal tissues remained viable for at least 2 hours and exhibited stable basal HCO 3-secretion and electrical parameters. Stimulation with PGE 2 and db-cAMP resulted in dose-related increases in both I SC and HCO 3-secretion ( P < .05) that were abolished by ouabain and anoxia. It is concluded (1) that human duodenal bulb biopsy samples maintain their inherent transport function in mini-Ussing chambers and (2) that by using this novel method it will be possible to define the transport events that modulate human duodenal secretion, in particular bicarbonate secretion, in both health and disease.

Carbon dioxide mediates duodenal mucosal alkaline secretion in response to luminal acidity in the anesthetized rat

Background & Aims: Acid exposure of the duodenum elicits various functional responses, e.g., an increased mucosal alkaline secretion. Despite low pH in luminal contents, the mucosal secretion of bicarbonate-rich fluid results in pH neutrality at the surface epithelium. It follows that it is probably not luminal pH that triggers the secretory response. The present study was undertaken to investigate if CO 2 could serve as an intermediate messenger between luminal acid and the mucosal secretory response. Methods: Experiments were performed on chloralose-anesthetized rats. The duodenal mucosal alkaline secretion was measured by in situ pH-stat titration. Results: Exposure of the duodenal mucosa to CO 2, administered either as a pregassed solution (pH 4, P CO 2 700 mm Hg) or as an acidified bicarbonate solution (pH 6.4, P CO 2 240 mm Hg), raised the alkaline output by approximately 65%. This response was blocked by the nitric oxide synthase inhibitor N G-nitro- L-arginine methyl ester (0.3 mmol/L intraluminally) but not by indomethacin (5 mg/kg intravenously). Conclusions: Exposure of the duodenal mucosa to solutions with high concentrations of CO 2 increases the mucosal alkaline secretion despite an almost neutral pH. Data indicate that the L-arginine/NO pathway is involved in the mediation of this response. GASTROENTEROLOGY 1998;115:680-685

Calcium signaling in cultured human and rat duodenal enterocytes.

Vagal stimuli increase duodenal mucosal HCO-3 secretion and may provide anticipatory protection against acid injury, but duodenal enterocyte (duodenocyte) responses and cholinoceptor selectivity have not been defined. We therefore developed a stable primary culture model of duodenocytes from rats and humans. Brief digestion of scraped rat duodenal mucosa or human biopsies with collagenase/dispase yielded cells that attached to the extracellular matrix Matrigel within a few hours of plating. Columnar cells with villus enterocyte morphology that exhibited spontaneous active movement were evident between 1 and 3 days of culture. Rat duodenocytes loaded with fura 2 responded to carbachol with a transient increase in intracellular calcium concentration ([Ca2+]i), with an apparent EC50 of approximately 3 microM. In a first type of signaling pattern, [Ca2+]i returned to basal or near basal values within 3-5 min. In a second type, observed in cells with enlarged vacuoles characteristic of crypt cell morphology, the initial transient increase was followed by rhythmic oscillations. Human duodenocytes responded with a more sustained increase in [Ca2+]i, and oscillations were not observed. Rat as well as human duodenocytes also responded to CCK-octapeptide but not to vasoactive intestinal polypeptide. Equimolar concentrations (100 nM) of the subtype-independent muscarinic antagonist atropine and the M3 antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide prevented the response to 10 microM carbachol, whereas the M1 antagonist pirenzepine and the M2 antagonists methoctramine and AF-DX 116BS had no effect at similar concentrations. Responses in rat and human duodenocytes were similar. A new agonist-sensitive primary culture model for rat and human duodenocytes has thus been established and the presence of enterocyte CCK and muscarinic M3 receptors demonstrated.

Variability in the composition of physiologic duodenogastric reflux

Duodenogastric reflux has long been associated with various diseases of the foregut. Even though bile is often used as a marker, duodenogastric reflux consists of other components such as pancreatic juice and duodenal secretions. The aim of this study was to investigate the occurrence of duodenogastric reflux, its components, and the variability of its composition in normal subjects. Twenty healthy volunteers (7 men and 13 women) whose median age was 24 years underwent combined 24-hour bilirubin and gastric pH monitoring and intraluminal gastric aspiration. All probes were placed at 5 cm below the lower border of the lower esophageal sphincter. Aspiration was performed hourly and at any time when bilirubin and/or pH monitoring showed signs of duodenogastric reflux. Elastase and amylase were measured in the aspirate. All volunteers had episodes of physiologic duodenogastric reflux. A total of 70 episodes of duodenogastric reflux were registered with a median of three episodes (range 1 to 8) per subject. Most bile reflux occurred separately from pancreatic enzyme reflux. Pancreatic enzyme aspirate was significantly more often associated with a rise in pH in comparison to bile reflux (P <0.01). Duodenogastric reflux is a physiologic event with varying composition. Both bile and pancreatic enzyme reflux frequently occur separately. These findings could explain the disagreement regarding assessment and interpretation of duodenogastric reflux in the past. Thus monitoring of duodenogastric reflux requires more than the detection of just one component.

Acid/Base Transporters in Human Duodenal Enterocytes

Background: Duodenal mucosal bicarbonate secretion serves as a key defensive factor against mucosal injury. The purpose of the present study was to isolate human proximal duodenal enterocytes and identify their inherent acid/base transporters that participate in duodenal alkaline secretion. Methods: Biopsy specimens were obtained from the duodenal bulb in 18 healthy volunteers. Individual duodenal epithelial cells were isolated by means of a combination of calcium chelation and collagenase. Intracellular pH (pHi) was measured by the pH-sensitive dye BCECF and dynamic fluorescence ratio imaging. Results: Cytologic and histologic examination confirmed that isolated cells were of epithelial origin. In HCO3

Human proximal duodenal alkaline secretion is mediated by Cl-/HCO3- exchange and HCO3- conductance.

The proximal duodenal epithelium secretes bicarbonate into an adherent mucus layer, thereby protecting the mucosa from injury by gastric acid and pepsin. While bicarbonate secretion is stimulated and inhibited by a number of agonists and antagonists, the apical anion transport pathways have not been addressed fully. The objective was to assess if apical Cl-/HCO3- exchange and Cl-:HCO3- conductance are involved in duodenal mucosal bicarbonate secretion (DMBS). In healthy volunteers, the proximal 4 cm of duodenum was isolated, perfused with either saline or 4,4'-diisothiocyano-2,2'-disulfonic acid (DIDS), and bicarbonate secretion and transepithelial potential difference (PD) were stimulated by either PGE2 or the phosphodiesterase inhibitor theophylline to increase cyclic AMP. Luminal DIDS abolished PGE2-stimulated DMBS, yet had no effect on the increase in PD and failed to significantly alter theophylline-induced DMBS and PD. Therefore, in human proximal duodenum, it appears that PGE2 and cAMP activate distinct HCO3- transport pathways likely involving a DIDS-sensitive Cl-/HCO3- exchanger and DIDS-insensitive HCO3- conductance.