Effects of endogenous and exogenous prostaglandins on glycoprotein synthesis and secretion in isolated rabbit gastric mucosa

Increased gastric mucus secretion alleviates non-steroidal anti-inflammatory drug-induced abdominal pain

Non-steroidal anti-inflammatory drugs (NSAIDs) can cause dyspeptic symptoms, including abdominal pain. Gastric mucus is important as the first line of defense against luminal irritants. In the present study, we investigated whether gastric mucus secretion could influence the severity of gastric mucosal injuries or NSAID-induced dyspeptic symptoms. Fifteen Helicobacter pylori-negative, healthy males were administered two types of NSAIDs, a non-selective cyclooxygenase inhibitor, naproxen (300 mg, twice a day), or a cyclooxygenase-2-selective inhibitor, etodolac (200 mg, twice a day), for 1 week in a crossover study, with an interval of ≥ 4 weeks. Study participants underwent endoscopic examinations before and after treatment. Pentagastrin-stimulated gastric secretions were collected for 10 min during endoscopic examinations, and were analyzed for gastric acid levels (mEq/10 min) and mucus output (mg hexose/10 min). The grade of gastric mucosal injury was assessed endoscopically. Among 29 subjects who completed the crossover study, 11 individuals reported abdominal pain following the administration of naproxen or etodolac for 1 week, as judged by elevated pain scores, while 18 individuals did not report abdominal pain. The occurrence of symptoms was not associated with the type of NSAIDs administered or the occurrence of erosive injury visualized by endoscopy. Gastric mucus secretion was significantly increased in subjects without drug-induced abdominal pain (P < 0.05), whereas it was significantly reduced in those with drug-induced abdominal pain (P < 0.05). In conclusion, the occurrence of NSAID-induced abdominal pain is associated with reduced levels of gastric mucus secretion rather than the occurrence of endoscopic mucosal injury.

Conjunctival goblet cells density and preservative-free tafluprost therapy for glaucoma: an in vivo confocal microscopy and impression cytology study

PURPOSE

To evaluate the density of conjunctival goblet cells (GCs) in glaucomatous patients treated with preservative-free (PF) tafluprost, using laser scanning confocal microscopy (LSCM) and impression cytology (IC).

METHODS

Thirty glaucomatous patients (30 eyes) naive for therapy and thirty healthy subjects (30 eyes) were enrolled. Conjunctiva was examined by means of Heidelberg Retina Tomography/Rostock cornea module. Afterwards, the specimens for IC were obtained. Patients were randomized to PF-tafluprost (Group 1) or preserved latanoprost (Group 2) and controls to the vehicle of latanoprost (Group 3) or physiological buffered saline solution (Group 4). Both LSCM and IC were performed at baseline, and after the 1st and 6th months of therapy, GC density (GCD) (cells/mm(2) ) was the main outcome measurement.

RESULTS

  Baseline. Mean GCD was 240.69 ± 25.43 and 232.65 ± 23.52, for LSCM, and 162.10 ± 23.44 and 164.71 ± 21.03 for IC in Group 1 and 2, respectively. GC density values were not significantly different in Group 3 and 4 (p > 0.05%). Month one. Mean GCD increased to 284.16 ± 43.88 and 230.62 ± 48.32 in Group 1 (p < 0.001) and to 297.86 ± 26.87 and 221.78 ± 43.02 in Group 2 (p < 0.05), measured with LSCM and IC, respectively. In Group 3, GCD decreased to 205.88 ± 25.04 and 139.54 ± 17.37 measured with LSCM and IC, respectively (p < 0.05). Month six. Mean GCD did not change in Group 1 (p > 0.05) whereas it decreased in Group 2 (p < 0.05), compared to month 1. In Group 3, GCD further decreased to 166.32 ± 22.31 and 120.76 ± 11.66, measured with LSCM and IC, respectively (p < 0.05); in Group 4, mean GCD did not change during the study period (p > 0.05).

CONCLUSIONS

Treatment with PF tafluprost was associated with an increase in conjunctival GCD in glaucomatous eyes naïve for therapy. Further studies are mandatory to verify this finding because its validation may have important consequences in the medical management of glaucoma.

Inhibition of ACh-stimulated exocytosis by NSAIDs in guinea pig antral mucous cells: autocrine regulation of mucin secretion by PGE2

The effects of indomethacin (IDM) and aspirin (ASA) on ACh (10 microM) -stimulated exocytotic events were studied in guinea pig antral mucous cells by using video optical microscopy. IDM or ASA, which inhibits cyclooxygenase (COX), decreased the frequency of ACh-stimulated exocytotic events by 30% or 60%, respectively. The extent of inhibition induced by ASA (60%) decreased by 30% when IDM or arachidonic acid (AA, the substrate of COX) was added. IDM, unlike ASA, appears to induce the accumulation of AA, which enhances the frequency of ACh-stimulated exocytotic events in ASA-treated cells. ONO-8713 (100 microM; an inhibitor of the EP1-EP4 prostaglandin receptors) and N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, HCl (H-89, 20 microM; an inhibitor of PKA) also decreased the frequency of ACh-stimulated exocytotic events by 60%. However, the supplementation of PGE(2) (1 microM) prevented the IDM-induced decrease in the frequency of ACh-stimulated exocytotic events. SC-560 (an inhibitor of COX-1) decreased the frequency of ACh-stimulated exocytotic events by 30%, but NS-398 (an inhibitor of COX-2) did not. Moreover, IDM decreased the frequency of exocytotic events stimulated by ionomycin, suggesting that COX-1 activity is stimulated by an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). ACh and ionomycin increased PGE(2) release in antral mucosal cells. In conclusion, in ACh-stimulated antral mucous cells, an increase in [Ca(2+)](i) activates Ca(2+)-regulated exocytotic events and PGE(2) release mediated by COX-1. The released PGE(2) induces the accumulation of cAMP, which enhances the Ca(2+)-regulated exocytosis. The autocrine mechanism mediated by PGE(2) maintains the high-level mucin release from antral mucous cells during ACh stimulation.

Expression and cytoprotective effect of protease-activated receptor-1 in gastric epithelial cells

Thrombin is a serine protease involved in many physiological functions and its receptor. the protease-activated receptor-1 (PAR-1), has a wide tissue distribution. We hypothesized that PAR-1 is expressed in gastric epithelial cells and that thrombin can modulate defence mechanisms through PAR-1. The rat gastric epithelial cell line (RMG1) and gastric biopsy specimens from gastritis patients were used in the study. Reverse transcriptase polymerase chain reaction analysis showed that the thrombin receptors PAR-1, PAR3 and PAR-4 are expressed by RGM1 gastric epithelial cell line. Immunohistochemical and electron microspcopic studies also showed PAR-1 expression in human gastric epithelial cells. Thrombin stimulated the secretion of mucin and prostaglandin E2 (PGE2) formation in RGM1 cells in a dose-dependent manner. PAR-1 agonist also stimulated PGE2 formation. In addition, thrombin significantly increases the expression of the PGE2 receptors EP2-R and EP4-R in RGM1 cells. In conclusion, the results of the present study showed for the first time that gastric epithelial cells express thrombin receptors and that these receptors may play a protective role in the gastric mucosa.

Sensory pathways and cyclooxygenase regulate mucus gel thickness in rat duodenum

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(2) injection or were challenged with pH 2.2 solution, with or without the vanilloid antagonist capsazepine, human CGRP-(8-37), N(G)-nitro-L-arginine methyl ester, and indomethacin. Other rats underwent sensory ablation with high-dose capsaicin pretreatment. Acid, bradykinin, capsaicin, and PGE(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.

The human prostanoid DP receptor stimulates mucin secretion in LS174T cells

This study demonstrates the localization of the prostaglandin (PG)D(2) receptor (DP) within the mucous-secreting globlet cells of the human colon by in situ hybridization, which suggests a role for DP in mucous secretion. Selective high affinity ligands were used, therefore, to evaluate DP regulation of mucous secretion in LS174T human colonic adenocarcinoma cells. The expression of hDP in LS174T cells was confirmed at the mRNA level by reverse transcriptase-polymerase chain reaction, and at the protein level by radioligand binding assays and signal transduction (cyclic AMP accumulation) assays. PGD(2) and the highly selective DP-specific agonist L-644,698 ((4-(3-(3-(3-hydroxyoctyl)-4-oxo-2-thiazolidinyl) propyl) benzoic acid) (racemate)), but not PGE(2) competed for [(3)H]-PGD(2)-specific binding to LS174T cell membranes (K:(i) values of 0.4 nM and 7 nM, respectively). The DP-specific agonists PGD(2), PGJ(2), BW245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropylhydantoin)), and L-644,698 showed similar potencies in stimulating cyclic AMP accumulation (EC(50) values: 45 - 90 nM) and demonstrated the expected rank order of potency. PGE(2) also elicited cyclic AMP production in this cell line (EC(50) value: 162 nM). The activation of cyclic AMP production by PGD(2) and L-644,698, but not PGE(2), was inhibited by the selective DP antagonist BW A868C. Thus, PGD(2) and L-644,698 act through hDP in LS174T cells. PGD(2), L-644,698 and PGE(2) (an established mucin secretagogue) potently stimulated mucin secretion in LS174T cells in a concentration-dependent manner (EC(50)<50 nM). However, BW A868C effectively antagonized only the mucin secretion mediated by PGD(2) and L-644,698 and not PGE(2). These data support a role for the DP receptor in the regulation of mucous secretion.

Intragastric administration of heparin enhances gastric ulcer healing through a nitric oxide-dependent mechanism in rats

Our preliminary finding indicated that intravenous (i.v.) injection of heparin increased gastric ulcer healing in rats. However, the anticoagulant action of i.v. heparin could produce complications in ulcer patients if the drug was used as an anti-ulcer agent. The present study aimed to investigate whether intragastric (i.g.) administration of heparin, known to have no anticoagulant activity, would have the similar ulcer healing effect and the relationship of this effect, if any, with nitric oxide (NO), a substance suggested to be important for ulcer healing. Heparin (100, 500, 1000 U/kg, i.g. ) administered once daily for 4 days accelerated the healing of gastric ulcer induced by acetic acid in Sprague-Dawley rats, which was accompanied by an increase in mucosal proliferation and regeneration at the ulcer margin, microvessel number both at the ulcer margin and base, and the thickness of mucus layer. Both activity and content, but not the mRNA of constitutive nitric oxide synthase (cNOS) in the gastric mucosa were enhanced. L-N(G)-nitroarginine methyl ester (L-NAME), an inhibitor of NOS activity blocked the cNOS activity activated by heparin and reversed the beneficial effects of heparin on ulcer healing. The bleeding time was not altered by i.g. heparin. These findings demonstrate that i.g. heparin promotes the healing processes of gastric ulcer. Such effect is suggested to act through the stimulation of mucosal cNOS activity. In addition, i.g. heparin is better than i.v. heparin without the potential anticoagulation effect.

Augmentative effects of L-cysteine and methylmethionine sulfonium chloride on mucin secretion in rabbit gastric mucous cells

BACKGROUND

Our previous study showed that L-cysteine (Cys) and methylmethionine sulfonium chloride (MMSC) inhibited ethanol-induced gastric mucosal damage and increased the amount of surface mucin in rats. This study examined whether Cys and MMSC augmented mucin secretion and changed distribution of mucin vesicles ultrastructurally in mucous cells by using primary cultured mucous cells from rabbit glandular stomach. Changes in intracellular cyclic adenosine 3',5'-monophosphate (cAMP) and in levels of cytosolic free Ca2+ were investigated by treatment with Cys and MMSC.

METHODS

Mucin content was measured by an enzyme-linked lectin assay. Transmission electron micrography was used to examine ultrastructural distribution of mucin granules. The amount of cAMP or levels of free Ca2+ were measured by enzyme immunoassay or by fura-2. 16,16-Dimethyl prostaglandin E2 (dmPGE2) or ATP was used as the positive control.

RESULTS

L-Cysteine and MMSC increased mucin secretion and decreased cellular mucin content. The same was noted for dmPGE2. Accelerated mucin granule movements toward the plasma membrane were shown by these agents. Intracellular cAMP increased with exposure to dmPGE2 for 20 min, while neither Cys nor MMSC increased cAMP. No increase in cytosolic free Ca2+ levels occurred after treatment with Cys or MMSC, but an increase was induced 10 s after the addition of ATP.

CONCLUSIONS

The present findings indicate that the increase in mucin secretion by Cys and MMSC was not mediated through the cAMP or Ca2+ signal transduction pathway, but might occur through non-receptor-mediated mechanisms.

EP4 receptor mediation of prostaglandin E2-stimulated mucus secretion by rabbit gastric epithelial cells

Prostaglandin (PG) E receptors are divided into four subtypes (EP1-EP4). We investigated the EP receptor subtype involved in PGE2-stimulated mucus secretion by rabbit gastric epithelial cells. Northern blot analysis revealed that epithelial cells express EP3 and EP4 receptor mRNAs, but neither EP1 nor EP2 receptor mRNAs were detected. PGE2, 11-deoxy-PGE1 (an EP3/EP4/EP2 agonist) and 16,16-dimethyl-PGE2 (an EP3/EP2/EP4 agonist) concentration-dependently promoted mucus secretion. In contrast, 17-phenyl-PGE2 (an EP3/EP1 agonist), sulprostone (an EP3/EP1 agonist), and butaprost (an EP2 agonist) failed to stimulate secretion. The effective concentrations of PGE2, 11-deoxy-PGE1, and 16,16-dimethyl-PGE2 were associated with their affinities for the EP4 receptor. In addition, PGE2, 11-deoxy-PGE1, and 16,16-dimethyl-PGE2 increased cyclic AMP (cAMP) production, but the other prostanoids had no effect. SQ22536 [9-(tetrahydro-2'-furyl)adenine; an adenylate cyclase inhibitor] inhibited both the increased cAMP production and mucus secretion induced by PGE2, 11-deoxy-PGE1, and 16,16-dimethyl-PGE2. H-89 (N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinoline sulfonamide; a protein kinase A inhibitor) also abolished the stimulatory effects of the prostanoids on mucus secretion, but calphostin C (a protein kinase C inhibitor) did not. These results indicate that PGE2 promotes mucus secretion by rabbit gastric epithelial cells, mediated through EP4 receptor stimulation and the subsequent activation of protein kinase A.

Relationship between gastric mucus synthesis, secretion and surface gel erosion measured in amphibian stomach in vitro

1. The layer of adherent mucus that protects the surface of the stomach reflects a dynamic balance between biosynthesis of glycoprotein, secretion of preformed mucus and erosion of the adherent gel layer. The present study is the first in which all these processes have been measured concomitantly and was undertaken to define interrelationships between the three parameters. 2. A chambered sac preparation of amphibian gastric mucosa is described. Biosynthesis was determined by specific incorporation of radiolabelled sugars into purified glycoprotein. Mucus secretion was determined by measuring the thickness of the adherent gel and erosion of the surface layer was assessed from the appearance of soluble mucin in the luminal solution. 3. 16,16-Dimethyl-prostaglandin (PG) E2 stimulated glucosamine incorporation by 10-fold, but did not alter the rate of incorporation of galactose. There was a rapid two-fold increase in the thickness of the adherent mucus layer but no change in the rate of erosion. Dibutyryl-cAMP also stimulated mucus release but, unlike PG, increased glycoprotein labelling by galactose. 4. Both distention or the application of a cholinergic agonist increased adherent mucus thickness. Stimulation of mucus release in response to carbachol was accompanied by a decrease in glycoprotein labelling by galactose. In contrast, the adrenergic agent noradrenaline decreased secretion but did not influence labelling. 5. These results indicate that biosynthesis and secretion of gastric mucus are subject to differential regulation. Moreover, the profile of incorporation of sugars in response to secretagogues also differs, indicating the need for caution when interpreting effects on glycoprotein biosynthesis.

Effects of PGE2 on amount and composition of high molecular weight glycoproteins released by human gastric mucous cells in primary culture

The aim of this study was to determine effects of prostaglandin E2 (PGE2) on amount and composition of high molecular weight glycoproteins (HMG), released by human gastric mucous cells in primary culture. PGE2 stimulated the release of HMG, as evidenced by measurement of total carbohydrate and protein content, in a concentration-dependent manner. At the maximally tested concentration of 10(-5) mol/l, the increase amounted to 53% and 85%, over controls, for carbohydrate and protein, respectively. The stimulated release was accompanied by alterations of HMG glycosylation. As detected by lectin-ELISA, there was a relative decrease in N-acetyl glucosamine and an increase in mannose and galactose content. The sialic acid content increased in parallel to the total carbohydrate content. These results suggest that PGE2 plays a regulatory role in the synthesis and secretion of HMG by human gastric mucous cells.

Prostaglandin E2 alters terminal glycosylation of high molecular weight glycoproteins, released by pig gastric mucous cells in vitro

The gastric mucus layer consists of high molecular weight glycoproteins (HMG). E-Type prostaglandins (PGs) stimulate total HMG release from isolated gastric mucous cells. We determined the effects of PGE2 on HMG glycosylation. Pig gastric mucous cells were cultured for 20 h with 1 mumol/l PGE2. Released HMG were isolated by gel chromatography and periodic acid-Schiff (PAS)-positive sugars and protein-bound [14C]GlcNAc were determined. Monosaccharides terminally linked to HMG oligosaccharide chains were monitored by lectin enzyme linked immunosorbent assay (ELISA): N-acetylglucosamine (GlcNAc) with Datura stramonium agglutinin, N-acetylgalactosamine (GalNAc) with soy bean agglutinin, fucose (Fuc) with Ulex europaeus I agglutinin and sialic acids (Sial) with Sambucus nigra agglutinin. PGE2 stimulated total HMG release, indicated by an increase of PAS-positive sugars to 170% and [14C]GlcNAc to 220% of controls. Terminal GlcNAc increased to 128%, GalNAc to 133%, Fuc to 165% and Sial to 182%. In addition to stimulation of total HMG release, PGE2 caused alterations of HMG glycosylation, which may modulate HMG viscosity and microbiological barrier function.

Drugs and endogenous ligands compete for receptor occupancy

Dietary and endogenous ligands compete with drugs for receptor occupancy and therefore should be considered during therapeutic interventions and during pharmacokinetic/pharmacodynamic modeling. When disease is the result of an overabundance of these natural ligands, antibodies and/or their Fab fragments may be useful as therapeutic agents to reverse the effects of the natural ligands.

The effect of 16,16-dimethyl prostaglandin E2 on proliferation of an intestinal goblet cell line and its synthesis and secretion of mucin glycoproteins

The effect of 16,16'-dimethyl prostaglandin E2 (dmPGE2) on the human colonic adenocarcinoma derived mucus-secreting goblet cell line HT29-18N2 was investigated. The proliferation rate of HT29-18N2 was increased by exposure to 10 or 100 microM dmPGE2. Exposure to 10 or 100 microM dmPGE2 caused a significant decrease in the rate of radiolabeled glucosamine incorporation into newly synthesized glycoproteins during an 8 or 24 h exposure. At concentrations as low as 1 microM, dmPGE2 accelerated the secretion of mucin glycoproteins as assessed by the release of newly synthesized radiolabeled glycoproteins, a mucin-specific enzyme-linked immunoassay and a whole-mount immunofluorescence assay. A 1 h exposure to dmPGE2 did not, however, result in a morphometrically detectable decrease in intracellular mucous granule stores or elicit any other readily detectable morphological change. The experimental results suggest elevated levels of PGs may contribute to the previously recognized decreases in intracellular mucin stores and shifts in the types of mucins species present at sites of mucosal inflammation in ulcerative colitis patients.

Regulation of canine gastric mucin synthesis and phospholipid secretion by acid secretagogues

Key components of the mucous gel include the glycoprotein mucin and surface-active phospholipids. In the present study, mucin production and release of the surface-active phospholipid phosphatidylcholine (PC) into the medium were measured with an isolated canine mucous cell culture system. Stimulation of glycoprotein synthesis in response to 10(-4) mol/L histamine (160% +/- 9% of control, P < 0.01), 10(-6) mol/L gastrin (129% +/- 7%, P < 0.01), and 10(-6) mol/L carbamylcholine (129% +/- 7%, P < 0.01) was observed by metabolic labeling, whereas prostaglandin E2 (PGE2) had no effect. The effect of histamine was blocked by the H2 receptor antagonist cimetidine but not the H1 receptor antagonist diphenhydramine (P < 0.01). Activators of adenylate cyclase and cyclic adenosine monophosphate analogs significantly stimulated mucin synthesis (P < 0.05). A 7.8% +/- 1.7% increase in mucin above basal levels after 24 hours was observed with a solid-phase immunoassay in control wells, whereas histamine, gastrin, and carbamylcholine increased total mucin by 14% +/- 0.7%, 17% +/- 4.3%, and 20.4% +/- 4%, respectively (all P < 0.01), and PGE2 had no significant effect. PC release was stimulated by the administration of histamine, carbamylcholine, gastrin (108%-110% of control, P < or = 0.05), and PGE2 (120% of control, P < 0.01). The acid secretagogues histamine, gastrin, and carbamylcholine stimulated mucin synthesis and PC release. PGE2 has no direct role in the synthesis of canine gastric mucin but stimulates release of surface-active phospholipids. The mechanisms responsible for acid secretion provide for the coordinated production of the primary layer of defense against the injurious effects of low pH.

Role of prostaglandin E2 in cholinergic-mediated glycoprotein synthesis in canine antrum

We studied the mechanism of cholinergic stimulation of mucin synthesis in canine antral explants, including the role of PGE2 as an intermediate messenger. Isolated antral mucosa was incubated with 10(-5) M carbachol (Cb), 10(-5) M indomethacin (IND), 10(-5) M pirenzepine (PZ), 10(-5) M Cb + 10(-5) M PZ, 10(-5) M Cb + 10(-5) M IND, and 10(-5) M IND + PGE2 (10(-8), 10(-7) and 10(-6) M) in the presence or absence of [3H]glucosamine. After 24 hr, total glycoprotein synthesis was quantitated by Sepharose-4B chromatography and by 10% TCA/1% PTA precipitation with lipid extraction. PGE2 released into the media was measured by radioimmunoassay (RIA). Cb significantly increased total glycoprotein synthesis and produced a significant increase in PGE2 release. The increase in glycoprotein synthesis and the release of PGE2 was blocked by the addition of muscarinic antagonist PZ. The addition of IND significantly inhibited glycoprotein synthesis and almost entirely suppressed PGE2 secretion. IND also inhibited the effect of Cb on glycoprotein synthesis and PGE2 release. Moreover, PGE2 (10(-6) and 10(-7) M) significantly increased the glycoprotein synthesis in the canine stomach. This suggests the coordinate participation of PGE2-releasing cell population in modulation of glycoprotein synthesis in gastric mucosa.

Dog gastric lipase: stimulation of its secretion in vivo and cytolocalization in mucous pit cells

Dog gastric lipase (DGL) secretion is stimulated in vivo by urecholine, pentagastrin, histamine, 16,16-dimethyl prostaglandin E2, and secretin. Under fasting conditions, DGL is irreversibly inactivated by gastric acid below pH 1.5; consequently, DGL output can be underestimated. This problem has been resolved by buffering the acid or by using an antisecretory drug such as omeprazole during stimulation. There is a clear parallelism between the secretion of DGL and of gastric mucus. This observation led to the present investigation of the cellular localization of DGL using immunofluorescence techniques. Results showed that DGL is cytolocalized in mucous pit cells of gastric glands. Pepsinogen is found in chief cells. To the authors' knowledge, this is the first description of an enzyme (gastric lipase) secreted by mucous-type gastric cells. In contrast to other species, gastric lipase of the dog is located in cardiac, fundic, and antral mucosae.

Pathogenesis of gastroduodenal injury due to nonsteroidal antiinflammatory drugs: implications for prevention and therapy

Nonsteroidal antiinflammatory drugs (NSAIDs) initiate gastroduodenal ulceration and promote complications such as bleeding and perforation by interfering with the ability of the proximal gastrointestinal tract to maintain its defensive capabilities. Mucosal defense is composed of three critical components: preepithelial, epithelial, and postepithelial. Preepithelial defense is composed of the mucous gel containing mucin, bicarbonate, and surface-active phospholipids. The epithelial component includes the surface cells, their apical tight junctions, and membrane transporters. Postepithelial defense is maintained by mucosal blood flow, which is essential for both defense and repair. NSAIDs interfere with each component of mucosal defense via direct toxic effects along with cyclooxygenase inhibition and depletion of endogenous prostaglandins. Although NSAID injury is dependent on luminal acid, attempts to prevent NSAID injury by acid suppression using H2-receptor antagonists in humans have had limited success, whereas complete inhibition of acid secretion with proton pump inhibition may have promise. Prostaglandins appear most effective for prevention of NSAID injury, sucralfate appears ineffective, and bismuth compounds have not been studied extensively. Recent evidence suggests that NSAID ulcers heal quickly with proton pump inhibitors compared with H2-receptor antagonists in patients who continue NSAID therapy.

Heparin-binding serum protein(s) is required for the protection of sialyltransferase released during the incubation of rat jejunal slices

Incubation of rat jejunal slices in Krebs-Ringer bicarbonate buffer (KRB) required the presence of heat-inactivated horse serum (HHS) in order to show time-dependent release of sialyltransferase into the medium. Sialyltransferase activity could not be detected in the medium when KRB alone or KRB supplemented with either albumin or glycerol was used in the incubations. The viability of the jejunal slices for up to 4 h of incubation was determined by studying the incorporation of glucosamine and leucine into acid-insoluble proteins. Supplementation of KRB with HHS had no beneficial effect on the rate of incorporation of leucine and glucosamine into proteins. KRB medium obtained after different periods of incubation contained higher trypsin-like activity than KRB medium containing HHS. Various antiproteases present as supplements to KRB resulted in the release of sialyltransferase activity from the jejunal slices. Among these antiproteases, alpha 1-proteinase inhibitor (alpha 1-PI) was the most effective. Also, HHS added to KRB immediately following incubation resulted in partial restoration of sialyltransferase activity in the medium, suggesting the presence of anti-proteolytic factors in HHS. The addition of increasing concentrations of heparin to incubations containing HHS caused a decrease in the medium sialyltransferase activity. The heparin-binding fraction (HBF) from HHS, when added to incubations, was able to protect the sialyltransferase released into medium. However, HHS depleted of its heparin-binding fraction by heparin-agarose affinity chromatography was unable to protect the sialyltransferase. HBF was separated into high- and low-molecular-mass fractions (fractions A and B respectively) by gel-filtration chromatography. The capacity to protect the released sialyltransferase was contained in fraction B. Fraction A contained multiple bands on SDS/PAGE and did not protect the enzyme. Fraction B contained a major protein band on the gel which corresponded to the migration of a similar band in human alpha 1-PI. HBF as well as fraction B isolated from HHS showed anti-trypsin-like activity. The results presented indicate that HHS contains a heparin-binding protein(s) similar to human alpha 1-PI which plays a role in the protection of sialyltransferase released from jejunal slices.

A new method of separation and quantitation of mucus glycoprotein in rat gastric mucus gel layer and its application to mucus secretion induced by 16,16-dimethyl PGE2

A method was established for recovering the mucus gel layer of rat gastric mucosa without damage to underlying surface epithelium. The mucus gel was solubilized by stirring the gastric mucosa in a solution of N-acetylcysteine (NAC), a mucolytic agent. Optimal mucus gel solubilization was possible by treatment with 2% NAC for 5 minutes at room temperature. Mucus glycoprotein was quantitatively extracted and measured from the mucus gel sample obtained by the NAC treatment. This treatment caused no damage to surface epithelial cells, as observed by a light microscope. Besides NAC, pronase solution was also adequate for solubilizing the mucus gel layer without any damage to the surface epithelium. However, extraction and measurement of mucus glycoprotein from the pronase-treated mucus gel sample was not possible due to contamination by high molecular hexose-containing substances which were eluted along with the mucus glycoprotein from the column of Bio-Gel A-1.5m. This NAC method was used to examine changes in mucus glycoprotein content in the mucus gel at one hour following the oral administration of 16,16-dimethyl prostaglandin E2. A significant increase in mucus glycoprotein of the gel was brought about by the prostaglandin treatment. Thus, the present method was suitable for estimating the amount of mucus secreted in to the mucus gel layer.

Gastroduodenal mucosal damage with salsalate versus aspirin: results of experimental models and endoscopic studies in humans

Animal models have identified multiple mechanisms of aspirin toxicity. Aspirin inhibits cyclooxygenase in the gastroduodenal mucosa leading to a decrease in endogenous prostaglandins. Prostaglandin mediated mucus and bicarbonate secretion, epithelial hydrophobicity, blood flow, and cellular proliferation are all decreased. Salicylates may cause direct cellular toxicity via inhibition of energy metabolism and membrane transport properties. Salicylate preparations have been designed to decrease gastroduodenal absorption. Endoscopic studies in humans have confirmed that buffering of aspirin does not ameliorate damage, but enteric coating does. Salicylsalicylic acid (salsalate) is an effective antirheumatic drug that bypasses gastric absorption and also avoids cyclooxygenase inhibition. In a randomized, single-blind, endoscopic comparison of salsalate versus enteric-coated aspirin, significantly less gastroduodenal damage was observed in volunteers after salsalate administration compared to enteric-coated aspirin. An endoscopic study in rheumatoid arthritics also confirmed the ability of salsalate to spare gastroduodenal mucosa when compared to naproxen administration. Salsalate may cause less gastroduodenal damage than enteric-coated aspirin based on the results of animal models and endoscopic studies in humans.

Regulation of mucus secretion by cells isolated from the rat gastric mucosa

1. A suspension of cells, containing about 30% mucous cells, was isolated from the rat fundic mucosa, and was pre-incubated with D-[6-3H]glucosamine. 3H-labelled material subsequently released into the medium was separated by Fast Protein Liquid Chromatography on a Superose 6 column. 2. A sharp peak of labelled high molecular weight material eluted from the column close to the void volume. This material was identified as mucous glycoprotein by its similar chromatographic behaviour to partially purified rat gastric mucous glycoprotein, by its resistance to complete degradation by papain and by its behaviour on treatment with dithiothreitol. On a caesium chloride density gradient the labelled material was virtually all located between densities of 1.35 and 1.53 g/ml. with the main peak at 1.40 g/ml. 3. A broad peak of lower molecular weight material was also eluted from the column. The release of this unidentified material did not seem to be closely associated with the release of mucous glycoprotein from the cells. 4. Release of mucous glycoprotein was stimulated by secretin (half-maximally effective concentration 2.3 nM, 84% stimulation above basal release at 100 nM), and by isoprenaline (half-maximally effective concentration 34 nM, 33% stimulation at 1 microM). Carbachol (0.5 nM) produced a significant (18-29%) stimulation of mucus secretion, but gastrin (100 nM), histamine (0.5 mM) and epidermal growth factor (200 nM) were without effect. 5. The preparation should prove useful in the identification of the agents which regulate gastric mucus secretion.