Stimulation of glycoprotein and protein synthesis in isolated pig gastric mucosal cells by prostaglandins

Effect of rebamipide on prostaglandin EP4 receptor gene expression in rat gastric mucosa

Prostaglandin E2 (PGE2) plays an important role in the regulation of gastric mucus secretion. We have previously shown that the prostaglandin EP4 receptor (EP4) gene is abundantly expressed in gastric mucus-producing cells. Furthermore, we have shown that EP4 is present in a rat normal gastric mucosal cell line (RGM1) and that PGE2 increases mucus secretion from these cells via EP4. Rebamipide, an anti-gastric ulcer agent, has been reported to promote gastric PGE2 production and mucus secretion. However, it is unclear whether rebamipide influences mucus secretion by altering expression of the EP4 gene. Therefore, we tested the effect of rebamipide on EP4 gene expression in the gastric mucosa. Seven-week-old Wistar rats received oral rebamipide (100 mg/kg) with and without water-immersion restraint stress (WRS). All rats were killed, and their gastric tissues were used to investigate the expression of mRNA for EP4 and cyclooxygenase types 1 and 2. The thickness of the gastric mucus layer was also measured. The effect of rebamipide on EP4 gene expression and PGE2 production in RGM1 cells was also investigated in vitro. Furthermore, the effect of PGE2 on cyclic adenosine monophosphate (cAMP) production by RGM1 cells with or without rebamipide was studied. Oral rebami-pide significantly increased EP4 gene expression in the gastric antrum but not in the corpus after WRS. Furthermore, it increased surface mucus thickness and suppressed ulcer formation in the gastric mucosa after WRS. In vitro, rebamipide significantly augmented EP4 gene expression in RGM1 cells, and PGE2 significantly increased the cAMP production by RGM1 cells incubated with rebamipide. Rebamipide promotes EP4 gene expression and may consequently increase the gastric mucus secretion via EP4 receptors in the rat antral mucosa.

Effects of PGE2 and of different synthetic PGE derivatives on the glycosylation of pig gastric mucins

The glycosylation of pig gastric mucins, discharged in response to prostaglandin (PG) E2 and to three synthetic PGE-derivatives (misoprostol, nocloprost, rioprostil) was compared. After a 20 h culture period in the absence or presence of 1 micromol/l of one of the PGs, mucins were isolated by gel chromatography and their glycosylation characterized by their linkage to a panel of lectins. For all tested PGs, a significantly increased lectin linkage to mucin glycoproteins of high molecular weight was detected; no significant effects were observed for low molecular weight glycoproteins. Within the stimulatory pattern, major effects were found for the linkage of peanut agglutinin and soybean agglutinin, suggesting predominant effects on the expression of galactose and N-acetyl-galactosamine. Only minor effects were found for sialic acid, mannose, N-acetyl-glucosamine and fucose expression, as evidenced by the linkage of Sambucus nigra agglutinin, Concanavalin A, Datura stramonium agglutinin and Ulex europaeus I agglutinin. All PGs exerted a similar stimulatory pattern. However, at the indicated concentration, misoprostol (281 +/- 36% of control) rendered a significantly higher overall effect than PGE2 (208 +/- 31%), whereas the increases induced by nocloprost (237 +/- 35%) and rioprostil (202 +/- 35%) were not significantly different from the PGE2 effects. These results, suggesting similar stimulatory effects of PGE2 and of the tested synthetic PGs on glycosylation of mucin oligosaccharides, discharged from mucous cells during an in vitro culture, may, at least in part, explain clinical findings that during an impairment of the endogenous PG synthesis, the tested synthetic PGs are effective exogenous substitutes for endogenous E-type prostaglandins and act as anti-ulcer drugs.

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.

Distribution of prostaglandin E receptors in the rat gastrointestinal tract

AIMS

In order to study the role of prostaglandin in the regulation of the gastrointestinal functions, gene expression of prostaglandin receptors along the rat gastrointestinal tracts were investigated.

METHODS

Rats were used for the study. The combination of counterflow elutriation separation of mucosal cells and Northern blot analysis was used to detect the gene expression of prostaglandin receptors in gastrointestinal tracts.

RESULTS

In small intestine and colon, prostaglandin E2 EP1 and EP3 receptor mRNAs were mainly localized in the deeper intestinal wall containing muscle layers. EP4 receptor gene expression, on the other hand, was detected in the intestinal mucosal layer. In the stomach, EP1 mRNA was detected in gastric muscle layers, whereas EP3 and EP4 receptor gene expression was mainly present in the gastric mucosal layer containing epithelial cells. In gastric epithelial cells, parietal cells were found to have both EP3 and EP4 receptors. At lower concentrations, prostaglandin E2 inhibited gastric acid secretion by parietal cells probably through EP4 receptors. At higher concentrations, however, it stimulated it. On the other hand, mucous cells possessed only EP4 receptor mRNA.

CONCLUSIONS

Thus, it is suggested that prostaglandin E2 modulates gastrointestinal functions through at least three different prostaglandin receptors (EP1, EP3, and EP4), each of which has a distinct contribution in the gastrointestinal tract.

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.

Cellular and chemical mediators of type 1 hypersensitivity in calves infected with Ostertagia ostertagi: histamine, prostaglandin D2, prostaglandin E2 and leukotriene C4

Plasma histamine, prostaglandin E2 (PG) D2, PGE2, and leukotriene (LT) C4 levels were determined in 26 Holstein steers before and after natural or experimental infection with Ostertagia ostertagi. Post-infection abomasal lymph was also assayed for PGD2, PGE2, and LTC4. Histamine determinations were performed on abomasal tissue from three locations. Results showed that: (1) tissue histamine levels increased in steers with type 2 ostertagiosis, (2) lymphatic PGD2 and PGE2 levels were increased, probably as a result of macrophage activity, (3) lymphatic LTC4 levels increased in steers with type 1 ostertagiosis, and were correlated with tissue eosinophilia, and (4) plasma levels of PGD2, PGE2, LTC4 and histamine were not useful for predicting worm burdens. These findings suggest a functional role for eosinophils and mast cells in the pathophysiology of ostertagiosis, through mediation of a type 1 hypersensitivity reaction.

Immunoglobulin E and type I hypersensitivity in bovine ostertagiosis

A series of experiments were performed to determine whether immunoglobulin E (IgE) and Type I hypersensitivity reactions might be involved in the immune response of cattle to infection with Ostertagia ostertagi. The following observations were made. (1) When calves were lightly infected, serum IgE levels paralleled worm burdens. However, in heavy infections, both serum and lymph IgE levels were inversely related to burdens of O. ostertagi. (2) Increases in mediators, especially histamine and leukotriene (LT) C4 were detected in tissue or lymph, and were associated with cellular changes indicative of hypersensitivity.

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.

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.

Effects of histamine and activators of the cyclic AMP system on protein synthesis in and release of high molecular weight glycoproteins from isolated gastric non-parietal cells

1. Glycoprotein and protein synthesis in and release from pig isolated, enriched gastric mucous cells were measured by the incorporation of N-acetyl-[14C]-D-glucosamine and [3H]-L-leucine, respectively, into cellular and released acid precipitable material. 2. Histamine and activators of the adenosine 3':5'-cyclic monophosphate (cyclic AMP) system maximally stimulated total protein and glycoprotein synthesis in and release from the cells at concentrations of histamine (10 microM), forskolin (10-100 microM), 3-isobutyl-1-methylxanthine (100 microM), and dibutyryl cyclic AMP (1-3 mM), respectively. In the presence of 3-isobutyl-1-methylxanthine (30 microM) histamine stimulation was enhanced. 3. As shown by gel chromatography, stimulation by histamine (100 microM), forskolin (10 microM), 3-isobutyl-1-methylxanthine (100 microM) and dibutyryl cyclic AMP (1 mM) resulted in a release of high molecular weight (approximately 2 x 10(6) daltons) glycoproteins from the cells. The histamine H2-receptor antagonist, ranitidine (100 microM), blocked the effect of histamine. 4. We conclude that cyclic AMP-dependent processes are involved in the regulation of protein and glycoprotein synthesis in and the release of high molecular weight (mucous) glycoproteins from pig gastric non-parietal cells and that histamine may be a physiological activator of this system.