Cell proliferation of the rat gastrointestinal mucosa after treatment with E2 prostaglandins and indomethacin

The frequency of arrested mitoses after vincristine injection was studied in the gastrointestinal mucosa of rats treated with either natural prostaglandin E2 (0.2-5.0 mg X kg-1, b.d.), 15-R-15 methyl prostaglandin E2 (2 mg X kg-1, b.d.) or indomethacin (1.0-3.0 mg X kg-1, b.d.). In addition to the mitotic index, morphometric measurements including the mucosal thickness and the thickness of the proliferative and functional zones of the gastric corpus, antrum and jejunum were performed. Natural prostaglandin E2, at the highest dose range, reduced significantly the mitotic index in the gastric antrum. Normal values were found in the gastric corpus and jejunum and in the antrum with the lower doses. The mitotic index was unaffected by treatment with 15-R-15 methyl prostaglandin E2. Natural prostaglandin E2 produced trophic changes (i.e. increased thickness and/or hyperplasia) in the antrum, functional epithelial zone of the gastric corpus and in the jejunum. More pronounced trophic changes were observed in the mucosa of rats treated with the analogue. Indomethacin reduced the mucosal thickness in all examined epithelia and lowered the mitotic index in the jejunum. It is concluded that the trophic effects of E2 prostaglandins on gastrointestinal epithelia are not caused by increased production of new cells. The reduced mitotic index observed in the antral mucosa of prostaglandin-treated rats could be secondary to a negative feedback from the hyperplastic epithelium. The antitrophic effects of the prostaglandin-synthesis blocker (indomethacin) indicates that endogenous prostaglandins may participate in the epithelial cell regulation of the gastrointestinal tract.     

Morphological and functional gastric cytoprotection by prostaglandin in rats receiving absolute ethanol orally.

Pretreatment with prostaglandins at non-antisecretory doses protects the gastric mucosa, including the parietal cells, from deep necrosis produced by intragastric administration of necrotising agents such as absolute ethanol. Whether the parietal cells also retained their ability to secrete acid when rats were pretreated with a prostaglandin, in spite of exposure to ethanol, was investigated. Gastric acid secretion was abolished 4 hours after ethanol, and secretion returned to control values only after 5-6 days. Pretreatment with a single, non-antisecretory dose of 16, 16-dimethyl prostaglandin E2 (dm PGE2) maintained acid secretion, in spite of exposure to absolute ethanol. Absolute ethanol caused histological changes - extensive gastric mucosal necrosis (through the muscularis mucosae), oedema, haemorrhages, polymorphonuclear infiltration, and formation of granulation tissue - that were maximal 24-48 hours after ethanol and persisted for 2 to 4 weeks. None of these changes were present in animals treated with the prostaglandin. It is concluded that a single oral pretreatment with dmPGE2 protects the gastric mucosa against not only the morphological damage of absolute ethanol (preventing necrosis, haemorrhages, and polymorphonuclear infiltration) but also the functional damage (maintaining the acid secretory function of parietal cells).     

Cell cycle distribution of proliferative and functional cells of the rat jejunum after treatment with oral E2 prostaglandins

Proliferative and functional epithelial cells were isolated from jejunal specimens of the rat by means of vibrational treatment combined with differential air insufflation. This method gave a good separation between superficial cells of the villi and the crypt cells, as evaluated by flow cytometry, morphology, cytology, and incorporation of radioactive thymidine into DNA. Groups of Sprague-Dawley rats (260 g) were treated twice daily for 11 days with oral placebo, 15(R)15-methyl-prostaglandin E2 in the range of 0.125-2 mg X kg-1, or 5 mg X kg-1 natural PGE2. Isolated crypt cells and superficial cells of the jejunal villi were then analysed by flow cytometry. Morphometric measurements were performed on sections of some jejunal specimens not submitted to vibrational treatment. The cell cycle distribution of crypt cells was unaffected by treatment with the prostaglandin analogue despite the presence of trophic changes. The proportion of crypt cells in G2/M phase was slightly but significantly reduced in rats given natural PGE2 compared with controls. The cell cycle distribution of villus cells was not affected by prostaglandin treatment. Trophic changes in the absence of increased DNA synthesis (S phase) or increased mitotic activity suggests that the hyperplasia observed after prostaglandin treatment is due to a reduced cell loss and/or slower migration time of epithelial cells.     

Effect of Prostaglandin E2 and 15(R)15 Methyl Prostaglandin E2 on Canine Gastric Parietal Cell

The effect of prostaglandin E2 (PGE2) and 15(R)15 methyl prostaglindin E2 (15(R)15 PGE2) on the gastric parietal cell was studied in seven and eight dogs, respectively. Another four dogs were used as controls. Gastric biopsies were examined by the electron microscope and the secretory activity of the parietal cells was assessed by morphometrically estimating the proportion of the parietal cell cytoplasm occupied by tubulovesicles as well as the ratio of extramitochondrial cytoplasm:mitochondria. Both 15(R)15 PGE2 and PGE2 increased the latter one hour after administration but only 15(R)15 PGE2 increased the proportion of tubulovesicles. The data suggest that secretory activity of parietal cells is impaired, especially after treatment with 15(R)15 GE2.     

Prostaglandins and vagal stimulation of gastric secretion in duodenal ulcer patients

The effects of a stable prostaglandin (PG) E2 analog (15-R-15 methyl PGE2) and aspirin, a potent inhibitor of cyclooxygenase, on modified sham-feeding (MSF)-stimulated gastric secretion and serum gastrin and pancreatic polypeptide (PP) levels were measured in patients with duodenal ulcer. PGE2 analog given orally significantly reduced gastric acid and pepsin secretion and suppressed serum PP but not gastrin responses to MSF. Suppression of PG generation in the gastric mucosa did not influence the secretory or hormonal responses to MSF. This study shows that endogenous PGs are not involved in the control of vagally stimulated gastric secretion, but exogenous PGE2 analog is an effective inhibitor of such secretion and merits clinical evaluation in the treatment of duodenal ulcer.     

Uremia in the rat affects gastric cell growth and differentiation

The aim of this study was to determine if hypertrophy of different tissues seen in uremic rats included gastrointestinal hypertrophy and an increase in parietal cell mass that might explain the increased acid secretion we previously reported. Chronic renal failure was induced by subtotal nephrectomy. Despite a lower total body weight, uremic rats had a significantly greater stomach weight (33%), corpus area (13%), corpus mucosal height (19%), and parietal (32%) and enterochromaffin-like (ECL, 54%) cell density, but a 16% decrease in mucous neck cell region height. These findings suggest that uremia leads to gastric stem cell stimulation with differentiation favoring parietal and ECL cells over mucous cells. In addition, in uremic rats there was an increase in height of the duodenal mucosa, but not of the ileal or transverse colon mucosa. In conclusion, the present study shows that uremia in the rat promotes hypertrophy of the stomach with cell differentiation favoring parietal cells over mucus cells. The increase in parietal cell mass may explain the increased acid secretion in these rats.     

Influence of long-term 16,16-dimethyl prostaglandin E2 treatment on the rat gastrointestinal mucosa

We performed acid secretory and histomorphometric studies in rats treated intragastrically with a regimen of 100 micrograms/kg or 5 micrograms/kg of 16,16-dimethyl prostaglandin E2, or of saline every 8 h for 21 days. All animals given the high-dose treatment developed a macroscopically visible enlargement of the ridge at the corpus-forestomach border, due to an increase in connective tissue and epithelial cell layer. Mucosal thickness was significantly increased in all parts of the stomach, the duodenum, and the proximal colon, but most markedly in the gastric antrum (+115%), where it was accompanied by a higher mitotic rate and hyperplasia of surface and foveolar mucous cells. Within the oxyntic area (corpus), high-dose prostaglandin treatment led to an increase in the number of surface and foveolar mucous cells and chief cells. In contrast, both the number of parietal cells and maximal acid output were not influenced. It is unlikely that the hyperplasia of gastric mucosa is mediated by gastrin since gastrin has no trophic effects on the rat antrum and disproportionally increases the parietal cell number of the oxyntic gastric glands.     

Alteration of the gastric mucosal glycoprotein in stress

Many studies have postulated the role of gastric acid and mucosal microcirculation in the development of gastric ulcer. We considered that gastric mucosal glycoprotein played one of the most important roles as the defensive factors of te gastric mucosa. The purpose of this study is to investigate te location and distribution of glycoprotein in the gastric mucosa in normal and stressful condition. Male Wistar rats, weighing 250 g were used as the experimental animals. Alternation and distribution of glycoprotein in the gastric mucosa were studied by light and electron microscopic examination employing HRP-labeled lectin such as PNA, DBA, ConA, RCA, SBA, WGA and UEA-1 as a parameter before and after the development of stress ulcer. Around Thirty percent scalding burn of the rat body surface area was created. At 2, 5 and 24 hours after burn induction, the gastric mucosa was examined. PNA-binding sites which were primarily localized to the generative cell zone in the control rat appeared to extend from the upper layer to the intermediate or the basal layer of the gastric mucosa in accordance with the development of stress ulcer after burn. Most of the binding sites was detected in the parietal cells particularly along microvilli in the intracellular secretory canaliculi. The tubulovesicular system in the parietal cells became stainable with PNA in the stress-loaded rats. Alternation and binding pattern of lectin, especially of PNA may indicate the local response of the parietal cells of the gastric mucosa against the stress.     

Calcium, calmodulin, and cyclic adenosine monophosphate modulate prostaglandin E2 release from isolated human gastric mucosal cells

We studied prostaglandin E2 (PGE2) release from isolated cells of the human gastric mucosa. Mucosal cells were enzymatically isolated from biopsy specimens of human fundic mucosa. The results from these crude cell preparations were compared to those obtained in fractions with enriched (65-80%) or depleted parietal cell content (3-7%) which were prepared from gastric mucosa obtained at surgery. PGE2 release in the enriched parietal cell fractions exceeded that from crude or parietal cell depleted preparations 3- and 13-fold, respectively. However, despite this quantitative difference, all preparations responded similarly to the test agents. Newly synthesized PGE2 was not stored intracellularly but was released into the incubation medium. Release increased linearly for 30 min. Addition of the calcium ionophore A23187 enhanced PGE2 release 4- to 5-fold. The effect of A23187 required the presence of extracellular Ca2+ (10(-3) mol/liter). Assuming that A23187 alters Ca2+ flux in gastric cells as it does in other cell systems our data indicate that increased Ca2+ influx enhances PGE2 release. Since calmodulin is of importance for intracellular Ca2+ action, the calmodulin antagonists trifluoperazine and W7 were tested. Both antagonists inhibited PGE2 release by 65-85%, trifluoperazine being slightly more effective. Activation of the adenylate cyclase system by forskolin or direct addition of (Bu)2cAMP, a stable cAMP-analog, also inhibited PGE2 release. We conclude that PGE2 is released from parietal and from nonparietal cells of the human gastric mucosa, although the major quantity is released from the light density fraction that is enriched in parietal cells. In parietal and nonparietal cells Ca2+ is of importance in the regulation of gastric mucosal PGE2 release and calmodulin seems to mediate this intracellular action of Ca2+. cAMP inhibits PGE2-release from gastric cells.     

Cimetidine and parietal cell regeneration in experimental wounds in rat gastric mucosa. A light and electron microscopic study

Cimetidine, 75 mg/kg body weight, was given twice daily by gastric tube to rats with experimental gastric ulcers. After 130 days' treatment the rats were killed, and sections from the wounds and normal mucosa were prepared for light and electron microscopy. Light microscopic studies showed that the regenerating mucosa in the wounds was thicker in the cimetidine-treated animals than in the controls. Stereological analyses demonstrated no differences in mean size of the parietal cells or in parietal cell volume density between the cimetidine-treated and the untreated groups, but an increase in the secretory surface density was detected in the parietal cells from rats that had been given cimetidine.     

Distribution of prostaglandins in gastric and duodenal mucosa of healthy subjects and duodenal ulcer patients: effects of aspirin and paracetamol.

The distribution of mucosal PGE2-like activity was determined by bioassay technique in the body and antrum of the stomach and in the duodenum of healthy subjects and duodenal ulcer patients before and after administration of aspirin, paracetamol, or histamine. In healthy subjects, the oxyntic, antral and duodenal mucosa was found to be capable of generating large amounts of PGE2, which were not significantly different from those found in duodenal ulcer patients. No correlation was found between the generation of PGE2 and gastric acid secretory status or serum gastrin level. Aspirin-and to a much lesser extent, paracetamol-caused a dramatic reduction in the ability of the gastric mucosa to biosynthesis PGE2 and this was accompanied by marked side-effects and injury to the gastric mucosa. Administration of histamine caused small but significant reduction in the biosynthesis of PGE2 but it was accompanied by marked mucosal damage. This study indicates that the gastric and duodenal mucosa is capable of generating PGE2-like activity which may be involved in the mechanism that protects the mucosa against the damage caused by aspirin.     

Prostanoid synthesis by cultured gastric and duodenal mucosa: Possible role in the pathogenesis of duodenal ulcer

Cultured duodenal mucosa obtained from normal subjects synthesized and secreted significantly less prostaglandin E2 (PGE2), 6-keto-PGF1 alpha, and thromboxane B2 (TXB2) than cultured gastric mucosa obtained from the same subjects. Accumulation of PGE2, 6-keto-PGF1 alpha, and TXB2--the stable metabolites of prostacyclin I2 and thromboxane A2, respectively--by cultured gastric mucosa obtained from 21 untreated patients with active duodenal ulcer was significantly lower than their respective accumulation by cultured gastric mucosa obtained from 14 normal subjects. Accumulation of all three prostanoids by cultured duodenal mucosa obtained from patients with active duodenal ulcer and from normal subjects was not significantly different. PGE2, 6-keto-PGF1 alpha, and TXB2 accumulation was five to six times higher than their respective content in fresh tissue before culture and was inhibited by flufenamic acid. These results suggest that a decrease in endogenous gastric prostanoid synthesis may have a role in the pathogenesis of peptic ulcer disease.     

Ultrastructure of inhibited parietal cells in the rat

In acutely vagotomized rats, gastric acid secretion was stimulated with a combination of carbachol and pentagastrin, and/or inhibited with picoprazole, cimetidine, or l-hyoscyamine. The animals were killed 1 or 3 h later. Using stereologic electron microscopic methods, the relative area of the secretory surface in the parietal cells and the mean size of these cells were estimated. The parietal cells in the superficial quarter of the oxyntic mucosa were larger than those at deeper levels of the mucosa. Moreover, the secretory surface was proportionally larger in the superficial cells than in the deep cells. Stimulation by carbachol and pentagastrin produced an increase in the secretory surface area. Inhibition of stimulated acid secretion by l-hyoscyamine reduced the secretory surface to the level of the unstimulated controls. Cimetidine, given at doses that inhibited stimulated acid secretion, did not alter the mean size of the secretory membrane. After inhibition by picoprazole, stimulated acid secretion was abolished, but the secretory membrane became significantly larger than after cimetidine inhibition. These divergent patterns of morphologic reactions probably reflect the different mechanisms of inhibition at the cellular level.     

Cyclooxygenase (COX) 1 and 2 in normal, inflamed, and ulcerated human gastric mucosa

BACKGROUND AND AIMS: Constitutive cyclooxygenase (COX) 1 is believed to mediate prostaglandin dependent gastric protection. However, gastric mucosa contains cells capable of expressing inducible COX-2. We therefore investigated COX-1 and COX-2 expression, localisation, and activity in normal and abnormal human gastric mucosa. METHODS: COX-1 and COX-2 distribution was investigated by light and electron microscopic immunohistochemistry and by western blot analysis, and their contribution to prostaglandin (PG)E(2) synthesis using selective enzyme inhibitors. RESULTS: There was strong parietal cell COX-1 and COX-2 immunoreactivity in all sections and isolated cells, with macrophage and myofibroblast reactivity in some sections. Immunostaining was specifically abolished by antigen absorption. Western blot analysis confirmed COX-1 and 2 expression. COX-1 and COX-2 immunostaining was increased in Helicobacter pylori gastritis, particularly the mid glandular zone and lamina propria inflammatory cells. This was associated with increased ex vivo PGE(2) synthesis (62.4 (13.5) pg/mg v 36.3 (15.5) pg/mg in uninflamed mucosa; p=0. 017) which was significantly inhibited by COX-1 but not COX-2 inhibition. Increased COX-2 immunostaining in macrophages, endothelial cells, and myofibroblasts (with reduced epithelial expression) was seen at the rim of ulcers. CONCLUSION: COX-2, as well as COX-1, is expressed by normal human gastric mucosa and is increased at the rim of ulcers. Although both are increased with H pylori, COX-1 contributes more than COX-2 to gastric PGE(2) production.     

Simultaneous measurement of in vitro gastroduodenal prostaglandin E2 synthesis and degradation in peptic ulcer disease

The ability of mucosal specimens from the stomach and duodenum to synthesize and degrade prostaglandin E2 has been determined in normal subjects and peptic ulcer patients. Significant reduction in fundic PGE2 synthesis capacity was observed in gastric ulcer patients. There was also significant reduction in the PGE2 degradation capacity of antral, fundic, and duodenal mucosal specimens in gastric ulcer patients. Patients with gastritis showed significant elevation of both antral and fundic PGE2 synthesis capacity compared with normal but no alteration in PGE2 degradation. No differences were observed in PGE2 synthesis and degradation rates in patients with duodenal ulcer. The results argue in favour of an association between impairment of PGE2 metabolism in the mucosa of patients with gastric but not duodenal ulceration.     

Effect of cholecystokinin and 16,16-dimethyl prostaglandin E2 on RNA and DNA of gastric and duodenal mucosa.

Fasted rats were injected with either cholecystokinin-octopeptide (CCK-OP), 20 mug per kg; 16,16-dimethyl prostaglandin E2 (16,16-dimethyl PGE2), 0.2 mg per kg; pentagastrin, 250 mug per kg, or saline every 8 hr for 48 hr. The rats were killed and the incorporation of [3H]thymidine into DNA as well as the total DNA and RNA content of the mucosa of the oxyntic gland area and the duodenum were determined. Pentagastrin increased DNA synthesis 60% (P less than 0.001) in gastric mucosa and 90% (P less than 0.001) in duodenal mucosa when compared with rates for saline controls. Neither CCK-OP nor 16,16-dimethyl PGE2 altered gastric mucosal DNA synthesis. Pentagastrin significantly increased the DNA and RNA content of both the gastric and duodenal mucosa. CCK-OP and 16,16-dimethyl PGE2 caused a slight but significant increase in duodenal DNA synthesis, CCK-OP did not significantly increase duodenal DNA content, and 16,16-dimethyl PGE 2 increased duodenal RNA but not DNA content. CCK-OP (20 mug per kg) in combination with pentagastrin did not alter the stimulation of gastric DNA synthesis but significantly decreased the effect of pentagastrin on duodenal DNA. A dose of CCK-OP (370 mug per kg) equimolar to 250 mug per kg of pentagastrin did not stimulate DNA synthesis in either tissue and significantly inhibited stimulation by pentagastrin in both tissues. Low doses of CCK-OP (2.5, 5.0, 10.0, 20.0 mug per kg) caused statistically significant increases in DNA synthesis and DNA content of the pancreas, but had no effect on either mucosa of the oxyntic gland area or duodenum. 16,16-Dimethyl PGE2 did not inhibit the stimulation of DNA synthesis or the increases in DNA and RNA content stimulated by pentagastrin. From these results it appears that: (1) moderate doses of CCK have a weak trophic effect in the duodenum but not in the stomach, (2) physiological doses of CCK-OP stimulated pancreatic DNA synthesis and increased pancreatic DNA content without affecting these parameters in the oxyntic gland area or duodenum in the same animals, (3) in the stomach and duodenum CCK is not as potent a trophic hormone as gastrin and inhibits, probably competitively, the trophic effects of gastrin, (4) 16,16-dimethyl PGE2 does not stimulate growth and does not interfere with the trophic response to gastrin even though it inhibits acid secretion, and (5) 16,16-dimethyl PGE2 increased the RNA content of duodenal mucosa indicating that it may stimulate activity resulting in hypertrophy.     

Intraduodenal instillation of acid and hyperosmolal solution suppresses pentagastrin-stimulated acid secretion but not histamine mobilization in the rat stomach

In chronic gastric fistula rats provided with a duodenal loop anastomosed to the jejunum (Roux-en-Y), maximal stimulation of acid secretion by continuous intravenous infusion of pentagastrin produced a 15-fold increase of gastric histidine decarboxylase activity. Intraduodenal instillation of 0.20 M HCl or 1200 mOsm X kg-1 solution of polyethylene glycol (PEG) inhibited the maximal acid response to pentagastrin by 61% and hyperosmolal (1200 mOsm X kg-1 of PEG solution) 0.20 M HCl by 79% but did not suppress the pentagastrin-induced increase in enzyme activity. Hence, instillation of HCl and/or hyperosmolal PEG solution in the duodenum depresses the responsiveness of the parietal cells to pentagastrin without interfering with pentagastrin-induced activation of gastric histamine formation.     

Enzyme Immunoassay of Gastric Luminal Prostaglandin E2 in Duodenal Ulcer Disease

A highly sensitive enzyme immunoassay was used to determine gastric juice prostaglandin E2 (PGE2) levels in control subjects with or without gastritis and in both active or inactive duodenal ulcer patients. Mean pentagastrin-stimulated PGE2 concentration was significantly lower in patients with duodenal ulcer than in control subjects considered as a whole group (with or without gastritis). However, no such difference was found between duodenal ulcer patients and controls showing histologically normal gastric mucosa. On the other hand, controls with chronic superficial gastritis had PGE2 levels significantly higher than those of histologically normal subjects and duodenal ulcer patients. Therefore, it seems unlikely that an absolute gastric PGE2 deficiency is involved in the pathogenesis of duodenal ulcer disease. However, the possibility that PGE2 synthesis could be deficient in relation to the prevailing level of mucosal inflammation cannot be excluded.     

Endogenous prostaglandins in peptic ulcer disease.

Plasma concentrations of prostaglandins E and F have been measured by radioimmunoassay in patients undergoing diagnostic upper intestinal endoscopy. The results fail to support a previously reported deficiency of plasma PGE in duodenal ulcer patients. Plasma prostaglandin concentrations failed to correlate with the parameters of gastric secretion studied; and were unaffected by histamine H2-receptor blockade or the activity of duodenal ulceration. During combined pentagastrin and insulin secretory studies there was a significant correlation between the outputs of PGE and acid into gastric juice.     

Rat gastric mucosal adenylyl cyclase.

Prostaglandin E1, epinephrine, secretin, and glucagon are known inhibitors of gastric acid secretion, and each agent stimulated mucosal membrane (600 X g pellet) adenylyl cyclase activity from the corpus of the rat stomach. This adenylyl cyclase activity was also stimulated by 5'-guanylyl-imidodiphosphate and sodium fluoride but not by guanosine-5'-triphosphate. By contrast, the gastric acid secretagogues, pentagastrin, histamine, and carbachol, had no effect on basal or prostaglandin E1-stimulated mucosal adenylyl cyclase activity. Most of the sodium fluoride- and hormone-stimulated adenylyl cyclase of the corpus mucosa was contained in the 600 X g membrane fraction. The enzyme exhibited Michaelis-Menten kinetics with respect to the concentration of ATP, with an apparent Km of 0.25 mM. Histamine did not stimulate rat mucosal adenylyl cyclase activity under a variety of conditions, but did stimulate the same enzyme in guinea pig gastric fundic mucosa, an enzyme also activated by prostaglandin E1. These studies do not support the hypothesis that cyclic AMP mediates the actions of gastric acid secretagogues on the parietal cell in the rat.