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Backgrounds and aimsWe studied the intestinotrophic hormone glucagon-like peptide-2 (GLP-2) as a possible therapy for non-steroidal anti-inflammatory drug (NSAID)-induced intestinal ulcers. Luminal nutrients release endogenous GLP-2 from enteroendocrine L cells. Since GLP-2 is degraded by dipeptidyl peptidase IV (DPPIV), we hypothesized that DPPIV inhibition combined with luminal administration of nutrients potentiates the effects of endogenous GLP-2 on intestinal injury.MethodsIntestinal injury was induced by indomethacin (10 mg/kg, sc) in fed rats. The long-acting DPPIV inhibitor K579 was given intragastrically (ig) or intraperitoneally (ip) before or after indomethacin treatment. L-Alanine (L-Ala) and inosine 5'-monophosphate (IMP) were co-administered ig after the treatment.ResultsIndomethacin treatment induced intestinal ulcers that gradually healed after treatment. Pretreatment with ig or ip K579 given at 1 mg/kg reduced total ulcer length, whereas K579 at 3 mg/kg had no effect. Exogenous GLP-2 also reduced intestinal ulcers. The preventive effect of K579 was dose-dependently inhibited by a GLP-2 receptor antagonist. Daily treatment with K579 (1 mg/kg), GLP-2, or L-Ala + IMP after indomethacin treatment reduced total ulcer length. Co-administration (ig) of K579 and L-Ala + IMP further accelerated intestinal ulcer healing.ConclusionDPPIV inhibition and exogenous GLP-2 prevented the formation and promoted the healing of indomethacin-induced intestinal ulcers, although high-dose DPPIV inhibition reversed the preventive effect. Umami receptor agonists also enhanced the healing effects of the DPPIV inhibitor. The combination of DPPIV inhibition and luminal nutrient-induced GLP-2 release may be a useful therapeutic tool for the treatment of NSAIDs-induced intestinal ulcers.

Copyright of Acta Medica Croatica is the property of Croatian Academy of Medical Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

Low-dose PG[E.sub.2] mimics the duodenal secretory response to luminal acid in mice. Am J Physiol Gastrointest Liver Physiol 286:G891 G898, 2004. First published February 5, 2004; 10.1152/ajpgi.00458.2003.--Luminal exposure to concentrated acid, the most accepted physiological stimulus for duodenal bicarbonate secretion (DBS), cannot be used with in vitro preparations due to potential tissue damage. We thus examined whether exposure to PG[E.sub.2], a well-characterized physiological duodenal secretagogue, could mimic the effects of acid perfusion. DBS was measured in C57/BL mice by pH-stat/back-titration and measurement of total dissolved C[O.sub.2] concentration ([C[O.sub.2].sub.t]). Anion transport inhibitor DIDS, anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), carbonic anhydrase inhibitor methazolamide, and nonselective cyclooxygenase inhibitor indomethacin were used to inhibit separate components of HC[O.sup.-.sub.3] secretory pathway. Baseline DBS was not altered by exposure to methazolamide (0.1 mM) but was slightly reduced by DIDS (0.5 mM). DBS and [C[O.sub.2].sub.t] increased after acid and PG[E.sub.2] exposure. DIDS (0.5 mM) and NPPB (0.2 mM) abolished acid-induced DBS increase. Methazolamide (0.1 mM) and DIDS inhibited acid-induced [C[O.sub.2].sub.t] increase. DIDS, NPPB, or methazolamide had little effect on DBS in response to high concentration PG[E.sub.2] (100 [micro]g/ml). Low concentration PG[E.sub.2] (1 [micro]/ml) increased DBS that was inhibited by DIDS, NPPB, and methazolamide. Pretreatment with indomethacin (5 mg/kg) inhibited DBS induced by acid exposure but not by PG[E.sub.2]. High-dose PG[E.sub.2] substantially increases DBS by a mechanism that appears to be different than secretory response to luminal acid perfusion. Secretory response to low-dose PG[E.sub.2], at least in terms of inhibitor profile, closely resembles secretion in response to perfusion of physiological acid concentrations and may be a useful stimulus for in vitro study of DBS in isolated mouse duodenum. luminal acid exposure; in vivo simulation; intestinal ion transport

We examined the effect of inhibition of [Na.sup.+]/[H.sup.+] exchange (NHE) on duodenal bicarbonate secretion (DBS) in rats to further understand DBS regulation. DBS was measured by using the pH-stat method and by using C[O.sub.2]-sensitive electrodes. 5-(N,N-dimethyl)-amiloride (50 [micro]M; DMA), a concentration that selectively inhibits the NHE isoforms NHE1 and NHE2, but not NHE3, did not affect DBS. Nevertheless, 3 mM DMA, a higher concentration that inhibits NHE1, NHE2, and NHE3, significantly increased DBS. Moreover, S1611 and S3226, both specific inhibitors of NHE3 only, or perfusion with [Na.sup.+]-free solutions, dose dependently increased DBS, as measured by pH-stat and C[O.sub.2]-sensitive electrode, without affecting intracellular pH. Coperfusion with 0.1 [micro]M indomethacin, 0.5 mM DIDS, or 1 mM methazolamide did not affect S3226-induced DBS. Nevertheless, coperfusion with 0.1 and 0.3 mM 5-nitro-2-(3-phenylpropylamino) benzoic acid, which inhibits the cystic fibrosis transmembrane conductor regulator (CFTR), dose dependently inhibited S3226-induced DBS. In conclusion, only specific apical NHE3 inhibition increased DBS, whereas prostaglandin synthesis. [Na.sup.+]-HC[O.sup.-.sub.3] cotransporter activation, or intracellular HC[O.sup.-.sub.3] formation by carbonic anhydrase was not involved. Because NHE3 inhibition-increased DBS was inhibited by an anion channel inhibitor and because reciprocal CFTR regulation has been previously shown between NHE3 and apical membrane anion transporters, we speculate that NHE3 inhibition increased DBS by altering anion transporter function. epithelial cells; cystic fibrosis transmembrane conductance regulator; back titration; S3226

Research was conducted to test the hypothesis that the duodenal hyperemic response to acid occurs through activation of capsaicin-sensitive afferent nerves with subsequent release of vasodilatory substances such as calcitonin gene-related peptide and nitric oxide. Findings showed that luminal acid, but not bradykinin, stimulates capsazepine-sensitive receptors on capsaicin-sensitive afferent nerves of rat duodenum.

The ability of the human spasmolytic peptide (hSP) in protecting the gastric cells from acidification was analyzed in rat gastric cells by in vivo microscopy and laser-Doppler flowmetry. The application of hSP to the luminal surface of the gastric mucosa protected the gastric surface cells from acidification during the process of luminal acidification. Furthermore, hSP reduced proton permeability in the gastric mucus gel.

The hypotheses that the gastric mucus gel, which is comprised of mucus and bicarbonate, protects gastric mucosal cells from luminal acids, and that acid protection is a function of mucus gel thickness, were tested using simultaneous measurements in vivo of the thickness of the gastric mucus gel and the intracellular pH of associated gastric epithelial cells. The results support the hypotheses since cell acidification rates were inversely proportional to the thickness of the mucus gel.

A mathematical method to study the movement of bicarbonate through the duodenal mucus indicates that the convection of fluids plays an important role in maintaining the pH of the intestine. The pH of the epithelial surface is almost neutral although a large amount of acid is secreted into it and the low levels of bicarbonate are inadequate to maintain the pH. A mucus barrier is formed into which the bicarbonate is secreted to neutralize the pH.

Copyright of Magyar Nőorvosok Lapja is the property of Hungarian Society of Obsterics & Gynaecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We studied the role of duodenal cellular ion transport in epithelial defense mechanisms in response to rapid shifts of luminal pH. We used in vivo microscopy to measure duodenal epithelial cell intracellular pH ([pH.sub.i]), mucus gel thickness, blood flow, and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] secretion in anesthetized rats with or without the [Na.sup.+]/[H.sup.+] exchange inhibitor 5-(NJV-dimethyl)-amiloride (DMA) or the anion transport inhibitor DIDS. During acid perfusion [pH.sub.i] decreased, whereas mucus gel thickness and blood flow increased, with [pH.sub.i] increasing to over baseline (overshoot) and blood flow and gel thickness returning to basal levels during subsequent neutral solution perfusion. During a second brief acid challenge, [pH.sub.i] decrease was lessened (adaptation). These are best explained by augmented cellular [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] up-take in response to perfused acid. DIDS, but not DMA, abolished the overshoot and phi adaptation and decreased acid-enhanced [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] secretion. In perfused duodenum, effluent total [CO.sub.2] output was not increased by acid perfusion, despite a massive increase of titratable alkalinity, consistent with substantial acid back diffusion and modest [CO.sub.2] back diffusion during acid perfusions. Rapid shifts of luminal pH increased duodenal epithelial buffering power, which protected the cells from perfused acid, presumably by activation of [Na.sup.+]-[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] cotransport. This adaptation may be a novel, important, and early duodenal protective mechanism against rapid physiological shifts of luminal acidity. intracellular pH; bicarbonate secretion; mucosal defense; mucus secretion; mucosal blood flow

Akiba, Yasutada, Osamu Furukawa, Paul H. Guth, Eli Engel, Igor Nastaskin, and Jonathan D. Kaunitz. Sensory pathways and cyclooxygenase regulate mucus gel thickness in rat duodenum. Am J Physiol Gastrointest Liver Physiol 280: G470-G474, 2001.--We previously showed that the duodenal hyperemic response to acid occurs through activation of capsaicin-sensitive afferent nerves with subsequent release of vasodilatory substances such as calcitonin gene-related peptide (CGRP) and nitric oxide. We then tested the hypothesis that similar factors regulate duodenal mucus gel thickness. Gel thickness was optically measured using in vivo microscopy in anesthetized rats. Duodenal mucosae were superfused with pH 7.0 buffer with vanilloid receptor agonist capsaicin, bradykinin, or [PGE.sub.2] injection or were challenged with pH 2.2 solution, with or without the vanilloid antagonist capsazepine, human CGRP-(8-37), [N.sup.G]-nitro-L-arginine methyl ester, and indomethacin. Other rats underwent sensory ablation with high-dose capsaicin pretreatment. Acid, bradykinin, capsaicin, and [PGE.sub.2] all quickly thickened the gel. Antagonism of vanilloid and CGRP receptors, inhibition of nitric oxide synthase, and sensory deafferentation delayed gel thickening, suggesting that the capsaicin pathway mediated the initial burst of mucus secretion that thickened the gel. Indomethacin abolished gel thickening due to acid, bradykinin, and capsaicin. Inhibition of gel thickening by indomethacin in response to multiple agonists suggests that cyclooxygenase activity is essential for duodenal gel thickness regulation. Duodenal afferent neural pathways play an important role in the modulation of cyclooxygenase-mediated physiological control of gel thickness. fluorescent microspheres; capsaicin-sensitive afferent nerves; bradykinin; capsazepine; indomethacin

Akiba, Yasutada, Paul H. Guth, Eli Engel, Igor Nastaskin, and Jonathan D. Kaunitz. Dynamic regulation of mucus gel thickness in rat duodenum. Am J Physiol Gastrointest Liver Physiol 279: G437-G447, 2000.--We examined the dynamic regulation of mucus gel thickness (MGT) in vivo in rat duodenum in response to luminal acid, cyclooxygenase (COX) inhibition, and exogenous [PGE.sub.2]. An in vivo microscopic technique was used to measure MGT with fluorescent microspheres in urethan-anesthetized rats. Duodenal mucosa was topically superfused with pH 7.0 or pH 2.2 solutions with or without [PGE.sub.2] and indomethacin treatments. Glycoprotein concentration of duodenal loop perfusates was measured with periodic acid/Schiff (PAS) or Alcian blue (AB) staining. MGT and perfusate glycoprotein concentration were stable during a 35-min perfusion with pH 7.0 solution. Acid exposure increased MGT and PAS- and AB-positive perfusate glycoprotein concentrations. Indomethacin pretreatment increased both PAS- and AB-positive perfusate glycoprotein at baseline; subsequent acid superfusion decreased perfusate glycoproteins and gel thickness. [PGE.sub.2] (1 mg/kg iv) simultaneously increased MGT and PAS-positive perfusate glycoprotein concentrations followed by a transient increase in AB-positive glycoprotein concentration, suggesting contributions from goblet cells and Brunner's glands. Parallel changes in MGT and perfusate glycoprotein concentration in response to luminal acid and [PGE.sub.2] suggest that rapid MGT variations reflect alterations in the balance between mucus secretion and exudation, which in turn are regulated by a COX-related pathway. Luminal acid and [PGE.sub.2] augment mucus secretion from goblet cells and Brunner's glands. fluorescent microspheres; perfusate glycoprotein concentration; indomethacin; periodic acid/Schiff staining; Alcian blue staining; Brunner's glands