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Lubiprostone, a bicyclic fatty acid, is used for the treatment of chronic constipation. No published study has addressed the effect of lubiprostone on intestinal ion secretion in vivo.The aim of this study was to test the hypothesis that lubiprostone augments duodenal HCO3 − secretion (DBS).Rat proximal duodenal loops were perfused with pH 7.0 Krebs, control vehicle (medium-chain triglycerides), or lubiprostone (0.1–10 μM). We measured DBS with flow-through pH and CO2 electrodes, perfusate [Cl−] with a Cl− electrode, and water flux using a non-absorbable ferrocyanide marker. Some rats were pretreated with a potent, selective CFTR antagonist, CFTRinh-172 (1 mg/kg, ip), 1 h before experiments.Perfusion of lubiprostone concentration dependently increased DBS, whereas net Cl− output and net water output were only increased at 0.1 μM, compared with vehicle. CFTRinh-172 reduced lubiprostone (10 μM)-induced DBS increase, whereas net Cl− output was also unchanged. Nevertheless, CFTRinh-172 reduced basal net water output, which was reversed by lubiprostone. Furthermore, lubiprostone-induced DBS was inhibited by EP4 receptor antagonist, not by an EP1/2 receptor antagonist or by indomethacin pretreatment.In this first study of the effect of lubiprostone on intestinal ion secretion in vivo, lubiprostone stimulated CFTR-dependent DBS without changing net Cl− secretion. This effect supports the hypothesis that Cl− secreted by CFTR is recycled across the apical membrane by anion exchangers. Recovery of water output during CFTR inhibition suggests that lubiprostone may improve the intestinal phenotype in CF patients. Furthermore, increased DBS suggests that lubiprostone may protect the duodenum from acid-induced injury via EP4 receptor activation.

Presence of taste receptor families in the gastrointestinal mucosa suggests a physiological basis for local and early detection of a meal. We hypothesized that luminal L-glutamate, which is the primary nutrient conferring fundamental umami or proteinaceous taste, influences mucosal defense mechanisms in rat duodenum. We perfused the duodenal mucosa of anesthetized rats with L-glutamate (0.1-10 mM). Intracellular pH ([pH.sub.i]) of the epithelial cells, blood flow, and mucus gel thickness (MGT) were simultaneously and continuously measured in vivo. Some rats were pretreated with indomethacin or capsaicin. Duodenal bicarbonate secretion (DBS) was measured with flow-through pH and C[O.sub.2] electrodes. We tested the effects of agonists or antagonists for metabotropic glutamate receptor (mGluR) 1 or 4 or calcium-sensing receptor (CaSR) on defense factors. Luminal L-glutamate dose dependently increased [pH.sub.i] and MGT but had no effect on blood flow in the duodenum. L-glutamate (10 mM)-induced cellular alkalinization and mucus secretion were inhibited by pretreatment with indomethacin or capsaicin. L-glutamate effects on [pH.sub.i] and MGT were mimicked by mGluR4 agonists and inhibited by an mGluR4 antagonist. CaSR agonists acidified cells with increased MGT and DBS, unlike L-glutamate. Perfusion of L-glutamate with inosinate (inosine 5'-monophosphate, 0.1 mM) enhanced DBS only in combination, suggesting synergistic activation of the L-glutamate receptor, typical of taste receptor type 1. L-leucine or L-aspartate had similar effects on DBS without any effect on [pH.sub.i] and MGT. Preperfusion of L-glutamate prevented acid-induced cellular injury, suggesting that L-glutamate protects the mucosa by enhancing mucosal defenses. Luminal L-glutamate may activate multiple receptors and afferent nerves and locally enhance mucosal defenses to prevent subsequent injury attributable to acid exposure in the duodenum. intracellular alkalinization; mucus secretion; bicarbonate secretion; monosodium glutamate; taste receptor doi: 10.1152/ajpgi.90605.2008

We hypothesized that the function of duodenocyte apical membrane acid-base transporters are essential for [H.sup.+] absorption from the lumen. We thus examined the effect of inhibition of [Na.sup.+]/[H.sup.+] exchanger-3 (NHE3), cystic fibrosis transmembrane regulator (CFTR), or apical anion exchangers on transmucosal C[O.sub.2] diffusion and HC[O.sup.-.sub.3] secretion in rat duodenum. Duodena were perfused with a pH 6.4 high C[O.sub.2] solution or pH 2.2 low C[O.sub.2] solution with the NHE3 inhibitor, $3226, the anion transport inhibitor, DIDS, or pretreatment with the potent CFTR inhibitor, [CFTR.sub.inh]-172, with simultaneous measurements of luminal and portal venous (PV) pH and carbon dioxide concentration ([C[O.sub.2]]). Luminal high C[O.sub.2] solution increased C[O.sub.2] absorption and HC[O.sup.-.sub.3] secretion, accompanied by PV acidification and PV PC[O.sub.2] increase. During C[O.sub.2] challenge, [CFTR.sub.inh]-172 induced HC[O.sup.-.sub.3] absorption, while inhibiting PV acidification. $3226 reversed [CFTR.sub.inh]-associated HC[O.sup.-.sub.3] absorption. Luminal pH 2.2 challenge increased [H.sup.+] and C[O.sub.2] absorption and acidified the PV, inhibited by [CFTR.sub.inh]-172 and DIDS, but not by $3226. CFTR inhibition and DIDS reversed HC[O.sup.-.sub.3] secretion to absorption and inhibited PV acidification during C[O.sub.2] challenge, suggesting that HC[O.sup.-.sub.3] secretion helps facilitate C[O.sub.2]/[H.sup.+] absorption. Furthermore, CFTR inhibition prevented C[O.sub.2]-induced cellular acidification reversed by $3226. Reversal of increased HC[O.sup.-.sub.3] lOSS by NHE3 inhibition and reduced intracellular acidification during CFTR inhibition is consistent with activation or unmasking of NHE3 activity by CFTR inhibition, increasing cell surface [H.sup.+] available to neutralize luminal HC[O.sup.-.sub.3] with consequent C[O.sub.2] absorption. NHE3, by secreting [H.sup.+] into the luminal microclimate, facilitates net transmucosal HC[O.sup.-.sub.3] absorption with a mechanism similar to proximal tubular HC[O.sup.-.sub.3] absorption. C[O.sub.2] absorption; bicarbonate secretion; portal venous PC[O.sub.2]

We hypothesized that duodenal [HCO.sup.-.sub.3] secretion alkalinizes the microclimate surrounding intestinal alkaline phosphatase (IAP), increasing its activity. We measured AP activity in rat duodenum in situ in frozen sections with the fluorogenic substrate ELF-97 phosphate and measured duodenal [HCO.sup.-.sub.3] secretion with a pH-stat in perfused duodenal loops. We examined the effects of the IAP inhibitors L-cysteine or L-phenylalanine (0.1-10 mM) or the tissue nonspecific AP inhibitor levamisole (0.1-10 mM) on AP activity in vitro and on acid-induced duodenal [HCO.sup.-.sub.3] secretion in vivo. AP activity was the highest in the duodenal brush border, decreasing longitudinally to the large intestine with no activity in stomach. Villous surface AP activity measured in vivo was enhanced by [PGE.sub.2] intravenously and inhibited by luminal L-cysteine. Furthermore, incubation with a pH 2.2 solution reduced AP activity in vivo, whereas pretreatment with the cystic fibrosis transmembrane regulator (CFTR) inhibitor [CFTR.sub.inh]-172 abolished AP activity at pH 2.2. L-Cysteine and L-phenylalanine enhanced acid-augmented duodenal [HCO.sup.-.sub.3] secretion. The nonselective P2 receptor antagonist suramin (1 mM) reduced acid-induced [HCO.sup.-.sub.3] secretion. Moreover, L-cysteine or the competitive AP inhibitor glycerol phosphate (10 mM) increased [HCO.sup.-.sub.3] secretion, inhibited by suramin. In conclusion, enhancement of the duodenal [HCO.sup.-.sub.3] secretory rate increased AP activity, whereas inhibition of AP activity increased the [HCO.sup.-.sub.3] secretory rate. These data support our hypothesis that [HCO.sup.-.sub.3] secretion increases AP activity by increasing local pH at its catalytic site and that AP hydrolyzes endogenous luminal phosphates, presumably ATP, which increases [HCO.sup.-.sub.3] secretion via activation of P2 receptors. duodenum; brush-border membrane; ELF-97 phosphate

We hypothesized that the function of duodenocyte apical membrane acid-base transporters are essential for H+ absorption from the lumen. We thus examined the effect of inhibition of Na+/H+ exchanger-3 (NHE3), cystic fibrosis transmembrane regulator (CFTR), or apical anion exchangers on transmucosal CO2 diffusion and HCO3- secretion in rat duodenum. Duodena were perfused with a pH 6.4 high CO2 solution or pH 2.2 low CO2 solution with the NHE3 inhibitor, S3226, the anion transport inhibitor, DIDS, or pretreatment with the potent CFTR inhibitor, CFTRinh-172, with simultaneous measurements of luminal and portal venous (PV) pH and carbon dioxide concentration ([CO21). Luminal high CO2 solution increased CO2 absorption and HCO3- secretion, accompanied by PV acidification and PV Pco2 increase. During CO2 challenge, CFTRinh-172 induced HCO3- absorption, while inhibiting PV acidification. S3226 reversed CFTRinh-associated HCO3- absorption. Luminal pH 2.2 challenge increased H+ and CO2 absorption and acidified the PV, inhibited by CFTRinh-172 and DIDS, but not by S3226. CFTR inhibition and DIDS reversed HCO3- secretion to. absorption and inhibited PV acidification during CO2 challenge, suggesting that HCO3- secretion helps facilitate CO2/H+ absorption. Furthermore, CFTR inhibition prevented CO2-induced cellular acidification reversed by S3226. Reversal of increased HCO3- loss by NHE3 inhibition and reduced intracellular acidification during CFTR inhibition is consistent with activation or unmasking of NHE3 activity by CFTR inhibition, increasing cell surface H+ available to neutralize luminal HCO3- with consequent CO2 absorption. NHE3, by secreting H+ into the luminal microclimate, facilitates net transmucosal HCO3- absorption with a mechanism similar to proximal tubular HCO3- absorption. [ABSTRACT FROM AUTHOR]

Background & Aims: The duodenal mucosa is exposed to Pco 2 >200 mm Hg due to the luminal mixture of gastric acid with secreted bicarbonate, which augments mucosal protective mechanisms. We examined the hyperemic response to elevated luminal Pco 2 in the duodenum of anesthetized rats luminally exposed to high co 2 saline to help elucidate luminal acid-sensing mechanisms. Methods: Blood flow was measured by laser Doppler, and intracellular pH of epithelial cells by measured by ratio microimaging. The permeant carbonic anhydrase (CA) inhibitor methazolamide, relatively impermeant CA inhibitor benzolamide, vanilloid receptor antagonist capsazepine, or sodium-hydrogen exchanger 1 (NHE-1) inhibitor dimethyl amiloride were perfused with or without the high co 2 solution. Results: The high co 2 solution increased duodenal blood flow, which was abolished by pretreatment with methazolamide or capsazepine or by dimethyl amiloride coperfusion. Sensory denervation with capsaicin also abolished the co 2 effects. Benzolamide dose-dependently inhibited co 2-induced hyperemia and at 100 nmol/L inhibited co 2-induced intracellular acidification. The membrane-bound CA isoforms IV, IX, XII, and XIV and cytosolic CA II and the vanilloid receptor 1 (TRPV1) were expressed in duodenum and stomach. Dorsal root ganglion and nodose ganglion expressed all isoforms except for CA IX. Conclusions: The duodenal hyperemic response to luminal co 2 is dependent on cytosolic and membrane-bound CA isoforms, NHE-1, and TRPV1. co 2-induced intracellular acidification was inhibited by selective extracellular CA inhibition, suggesting that co 2 diffusion across the epithelial apical membrane is mediated by extracellular CA. NHE-1 activation preceding TRPV1 stimulation suggests that luminal co 2 is sensed as H+ in the subepithelium. [Copyright &y& Elsevier]

The duodenum is the site of mixing of massive amounts of gastric H+ with secreted HCO3−, generating CO2 and H2O accompanied by the neutralization of H+. We examined the role of membrane-bound and soluble carbonic anhydrases (CA) by which H+ is neutralized, CO2 is absorbed, and HCO3− is secreted. Rat duodena were perfused with solutions of different pH and with or without a cell-permeant CA inhibitor methazolamide (MTZ) or impermeant CA inhibitors. Flow-through pH and electrodes simultaneously measured perfusate and effluent pH and . High CO2 (34.7 kPa) perfusion increased net CO2 loss from the perfusate compared with controls (pH 6.4 saline, ) accompanied by portal venous (PV) acidification and increase. Impermeant CA inhibitors abolished net perfusate CO2 loss and increased net HCO3− gain, whereas all CA inhibitors inhibited PV acidification and increase. The changes in luminal and PV pH and [CO2] were also inhibited by the Na+–H+ exchanger-1 (NHE1) inhibitor dimethylamiloride, but not by the NHE3 inhibitor S3226. Luminal acid decreased total CO2 output and increased H+ loss with PV acidification and increase, all inhibited by all CA inhibitors. During perfusion of a 30% CO2 buffer, loss of CO2 from the lumen was CA dependent as was transepithelial transport of perfused 13CO2. H+ and CO2 loss from the perfusate were accompanied by increases of PV H+ and tracer CO2, but unchanged PV total CO2, consistent with CA-dependent transmucosal H+ and CO2 movement. Inhibition of membrane-bound CAs augments the apparent rate of net basal HCO3− secretion. Luminal H+ traverses the apical membrane as CO2, is converted back to cytosolic H+, which is extruded via NHE1. Membrane-bound and cytosolic CAs cooperatively facilitate secretion of HCO3− into the lumen and CO2 diffusion into duodenal mucosa, serving as important acid–base regulators. [ABSTRACT FROM AUTHOR]

Phorbol esters induce inflammation in rodents by activating protein kinase C. We determined whether nuclear factor-kappaB (NF-kappaB) and tumor necrosis factor-alpha (TNF-alpha) play role in the formation of gastric ulcer induced by phorbol-12-myristate-13-alphacetate (PMA) in rats. Subserosally injected PMA dose-dependently induced gastric mucosal ulcer. Activation of NF-kappaB in the gastric mucosa corresponding to the PMA injection sites was observed before the ulcers became obvious as assessed by an in situ fluorescence DNA binding assay and electrophoretic mobility shift assay. The NF-kappaB activation and subsequent ulcer formation were significantly inhibited by injection of pyrrolidine dithiocarbamate, proteasome inhibitor (MG132), or NF-kappaB decoy. Antibody against TNF-alpha significantly inhibited ulcer formation without attenuating NF-kappaB activation. These results suggest that both NF-kappaB activation followed by TNF-alpha release contribute to tissue damage in PMA-induced gastric ulcer formation. [ABSTRACT FROM AUTHOR]

A 52-year-old man underwent abdominoperineal resection of the rectum, a partial hepatectomy, and intrahepatic arterial infusion chemotherapy for rectal cancer and liver metastases in 2001. Due to recurrent liver metastases, additional hepatectomies were performed in 2003 and 2005. He then underwent radiofrequency ablation therapy and systemic chemotherapies with mFOLFOX6 and FOLFORI. In July 2007, positron emission tomography (PET) and computed tomography (CT) revealed a high level of (18)F-fluorodeoxyglucose (FDG) accumulation in the liver. After 6 cycles of chemotherapy with bevacizumab plus mFOLFOX6, the FDG accumulation disappeared. The multidisciplinary therapy was effective, yielding long term survival of over 8 years.