Study of the damaging effects of acetazolamide on gastric mucosa in rats

The present study demonstrated that acetazolamide (100 and 200 mg/kg, s.c.) induced severe gastric hemorrhagic ulceration in rats. The ulceration was aggravated by oral administration of HCl, but was inhibited by NaHCO3. Furthermore, the severity of ulceration was also decreased by pretreatment with methysergide, chlorpheniramine, or cimetidine. These protective effects were accompanied by an increase in serotonin and histamine released from the stomach. Acetazolamide injection also increased the protein level but reduced the sialic acid content in the gastric secretion, indicating that the gastric mucosal barrier may have been damaged. Prostaglandin E2 content of the gastric mucosa was not affected by the drug; however, carbonic anhydrase activity was markedly reduced in a dose-dependent manner. Thus, it is suggested that the ulceration induced by acetazolamide is mainly due to the inhibition of carbonic anhydrase activity and mucus secretion. The increase in serotonin and histamine release also may have been the contributing factors for gastric ulcer formation.     

Homeostasis in the gastric mucosa and blood circulation. Part 1. Mechanisms of the adequate blood flow maintenance in the gastric mucosa]

The increase of mucosal blood flow in response to food entrance into stomach or different irritant action is the component of gastric mucosal defence barrier. Sufficient blood flow ensures normal acid-bicarbonate balance in gastric mucosa, supports the healing process and prevents superficial damages from developing into deep ones. Capsaicin-sensitive afferent nerve fibers play the large role in the blood flow regulation. The influence of these nerve fibers on the gastric blood flow is mediated by the calcitonin-gene related peptide. This peptide released from peripheral afferent terminals improves microcirculation in stomach walls. Moreover nerve impulses from afferent neurons modulate parasympathetic activity that in turn induces the increase of gastric mucosal blood flow through both choilinergic and noncholinergic mechanisms. The gastric mucosal blood flow may be also regulated by humoral and paracrine metabolites. Nitric oxide and prostaglandines are the most important low molecular weight compounds. They play the main role in the maintenance of the basal gastric mucosal blood flow and in the development of hyperemic responses to harmful agents.     

Effect of omeprazole on secretion,synthesis and the gene expression of pepsinogen in the guinea pig stomach mucosa

The effects of omeprazole, a proton pump inhibitor, on gene expression, protein synthesis, intracellular storage and secretion of pepsinogen in guinea pig stomach were investigated. After treatment with omeprazole for five days, acid and pepsinogen secretion into the gastric lumen was significantly reduced. Concomitant with this, there was an increase in intracellular pepsinogen as demonstrated by increased pepsin activity in the gastric mucosa, more intense immunohistochemical staining by antibodies specific of pepsinogen and accumulation of secretory granules in the cells producing pepsinogen. In these cells, the amount for pepsinogen mRNA was reduced as revealed by Northern blotting and in situ hybridization. Ultrastructurally the endoplasmic reticulum of these cells was poorly developed, the findings being consistent with a reduction in protein synthesis. It appears that omeprazole inhibits the secretion of pepsinogen, increasing the intracellular store and leading to the reduction in gene expression probably by a feedback mechanism and consequent reduction in pepsinogen synthesis. Since these changes were most evident in the acid-secreting fundic gland mucosa, as compared with other mucosae secreting only pepsinogen, namely pyloric and duodenal mucosa, it appears probable that these changes are linked with omeprazole-induced reduction in the acid secretion.     

The contribution of Jan Evagelista Purkyn? to knowledge of the morphology and function of the gastric mucosa

Histological studies of the gastric mucosa led Purkyn? to the discovery of the cell as a fundamental structural unit of an organ (1837). This study led Purkyn? to draw conclusions about the physiological role of the gastric mucosa in protein digestion. These conclusions included the activation of pepsinogen, the buffering role of saliva and bile, and the production of hydrochloric acid. Purkyn? was thus the first to provide a general concept of the role of the stomach in food digestion.     

Effects of ethanol alone or after pretreatment with 20% ethanol on phospholipid metabolism in rat gastric mucosa

Changes in phospholipid metabolism in gastric mucosa caused by instillation of absolute ethanol (a cell-damaging agent) into the stomach of rats and the effects of pretreatment with 20% ethanol (a mild irritant) were investigated by using radioisotope-labeled fatty acids and glycerol. The labeled precursors were incorporated mainly into phosphatidylcholine and triacylglycerol, and also to lesser extents into phosphatidylethanolamine and phosphatidylinositol + phosphatidylserine. The instillation of absolute ethanol reduced the incorporation of fatty acids and glycerol into phospholipids within 15 min, indicating the inhibition by ethanol of de novo synthesis of phospholipids. Pretreatment with 20% ethanol caused the incorporation of fatty acids into phospholipids to be maintained after absolute ethanol instillation. These results suggest that the pretreatment with 20% ethanol may protect the cellular synthetic activity of phospholipids against damage by absolute ethanol. The incorporation of fatty acids into the free fatty acid fraction, monoacylglycerol and diacylglycerol was increased by absolute ethanol instillation, suggesting damage to the blood vessels of the gastric mucosa, and these changes were inhibited to some extent by the pretreatment with 20% ethanol.     

Histochemical study of carbonic anhydrase and HCO3(-)-stimulated adenosine triphosphatase in the rat stomach during hydrochloric acid secretion]

By means of histochemical methods it was established that carboanhydrase of the parietal cells of fundal glands and HCO-3 stimulated ATP-ase of the rat's gastric mucosa capillaries disposed next to the parietal cells were activated by food and histamine. The obtained data confirm the idea of the multicellular functional essembly sustaining HCL secretion (R. I. Salganik, 1974). Should gastrin induce the formation of histamine in endocrinous cells and the histamine activate carboanhydrase in parietal cells, our data confirm the supposition that HCO-3-ions stimulate ATP-ase sustaining the exchange between HCO-3-cells and C1- of blood to form HCl in the endothelial cells of blood capillaries adjacent to the parietal cells.     

Certain Mechanisms regulating cell renewal in the gastric mucosa in peptic ulcer

A study was made of the effect of an aqueous extract of human gastric mucosa on the mitotic activity of the surface epithelium of the mouse stomach. The extract was found to exert a statistically significant inhibitory action. An extract from the mucosa of the stomach resected for duodenal ulcer exerted a more pronounced inhibitory action as compared with an extract from the stomach resected for gastric ulcer. This fact may be accounted for by a greater content of mature differentiated cells in duodenal ulcer. Tissue-specific action of gastric chalone is indicated by the absence of mitotic inhibition in the small intestinal mucosa.     

Increase of intracellular pH in secreting frog gastric mucosa

A method of estimation of pH in frog gastric mucosa by measuring the apparent creatine kinase equilibrium was studied. In a resting, in vitro preparation of frog stomach the intracellular pH was found to increase linearly with an increase in the serosal pH. This increase was also accompanied by an increase in the apparent equilibrium constant of the creatine kinase reaction. A similar increase was found when the resting mucosa was stimulated with histamine plus theophylline. During this procedure the total content of adenine nucleotides and creatine plus creatine phosphate remained constant.     

Combined effects of neurotransmitters upon secretory function of the rat stomach at different functional states of the gastric mucosa

Peculiarities of the combined effects of acetylcholine (ACh) and serotonin (St) on the pattern of histamine (His)-induced gastric secretion were studied on intact rats and rats with gastric impairments. Destructive and hemorrhagic changes of the gastric mucosa were modeled by i.p. injections of noradrenaline. The gastric secretory function was estimated using a perfusion technique. It was shown that the above stressor influence resulted in impairment of 20–60% of the gastric mucosa surface. Combined action of ACh, St, and His in intact animals revealed a dominating effect of St on acid secretion. Acetylcholine and St modulated the secretory activity of main cells, but their combination exerted no clear effect on pepsinogen secretion. Serotonin, if used against the background of His injection, restrained acid and pepsin secretions. In the animals with structural and hemorrhage disturbances of the gastric mucosa, the secretion indices characterazing combined action of the neurotransmitters decreased.     

Premature induction of pepsinogen in developing rat gastric mucosa by hormones

Daily injection of ACTH into rats from the age of 9 days caused precocious development of peptic activity in the gastric mucosa. A single injection of hydrocortisone into rats aged 2 to 9 days also evoked premature development of peptic activity in the gastric mucosa. The patterns on polyacrylamide gel electrophoresis of pepsinogen from adults and from infants treated with hormone were quite similar but differed from that of untreated infants. Enzyme from the gastric mucosa of adult rats and enzyme evoked with hormones were more stable than that from infant rats.     

L-carnitine protects gastric mucosa by decreasing ischemia-reperfusion induced lipid peroxidation.

Studies have shown that reactive oxygen metabolites and lipid peroxidation play important roles in ischemia-reperfusion injury in many organs such as heart, brain and stomach. The aim of this study is to evaluate the antioxidant effect of L-carnitine on gastric mucosal barrier, lipid peroxidation and the activities of antioxidant enzymes in rat gastric mucosa subjected to ischemia-reperfusion injury. Rats were subjected to 30 min of ischemia followed by 60 min of reperfusion. L-carnitine (100 mg/kg), was given to rats intravenously five minutes before the ischemia. In our experiment, lesion index, thiobarbituric acid reactive substances, prostaglandin E2 and mucus content in gastric tissue were measured. The results indicated that the lesion index and the formation of thiobarbituric acid reactive substances increased significantly with the ischemia-reperfusion injury in the gastric mucosa. L-carnitine treatment reduced these parameters to the values of sham operated rats. The tissue catalase and superoxide dismutase activities and prostaglandin E2 production decreased significantly in the gastric mucosa of rats exposed to ischemia-reperfusion. L-carnitine pretreatment increased the tissue catalase activity and prostaglandin E2 to the levels of sham-operated rats but did not change superoxide dismutase activity. There were no significant difference in glutathione peroxidase activity and mucus content between the groups in the gastric mucosa. In summary, L-carnitine pretreatment protected gastric mucosa from ischemia-reperfusion injury by its decreasing effect on lipid peroxidation and by preventing the decrease in prostaglandin E2 content of gastric mucosa.     

Effects of phenothiazines on acid secretion in the toad gastric mucosa

The effect of phenothiazine antipsychotic drugs on acid secretion was investigated in the isolated toad gastric mucosa. The acid secretory responses induced by maximal doses of histamine, carbachol and theophylline were all inhibited in a similar fashion by chlorpromazine. The ID50 was between 300 and 600 microM. Histamine-stimulated H+ secretion was also inhibited by trifluoperazine. Soluble cyclic AMP-dependent protein kinase activity was not significantly affected by 300 microM chlorpromazine. Microsomal (H+ + K+)-ATPase activity was significantly reduced by chlorpromazine. The results indicate that phenothiazines can inhibit acid secretion in the toad gastric mucosa and that inhibition of the gastric (H+ + K+)-ATPase may be involved in the mechanism of action.     

A comparative study of two kinds of cathepsin D-type proteinases from rat gastric mucosa

The localization of cathepsin D-like acid proteinase in the rat stomach and other tissues was studied, and its biochemical properties were compared with those of rat gastric cathepsin D (EC 3.4.23.5). Cathepsin D-like acid proteinase existed overwhelmingly in the mucosal layer and was hardly detected in the gastric juice. Its subcellular distribution profile was very similar to that of acid phosphatase, but not to that of pepsinogen. This proteinase-like enzyme activity was also found in rat splenic extract. These results strongly suggest that the proteinase is a lysosomal enzyme. In addition, cathepsin D-like acid proteinase demonstrated an in vitro transition of molecular species during storage at -30 degrees C. Although this molecular change was distinctive in ion-exchange column chromatography and susceptibility to some enzyme inhibitors, it was not accompanied by a significant decrease in molecular weight. To compare cathepsin D-like acid proteinase with ordinary cathepsin D, gastric cathepsin D was newly purified to apparent homogeneity in polyacrylamide gel electrophoresis. Its biochemical properties demonstrate that this is a true cathepsin D in rat gastric mucosa. Moreover, this cathepsin D activity was not abolished by treatment with antiserum specific to cathepsin D-like acid proteinase or pepsinogen. From these results, we can conclude that the proteinase is a lysosomal acid proteinase different from newly purified gastric cathepsin D.     

Sodium-iodide symporter mediates iodide secretion in rat gastric mucosa in vitro

In vivo studies on rats have demonstrated that considerable amounts of iodide are transported from the bloodstream into the gastric lumen. The mechanisms for and functional significance of this transport are poorly understood. Active (driven by Na(+)/K(+)-ATPase) iodide transport into thyroid follicular cells is mediated by the sodium-iodide symporter (NIS), which is also abundantly expressed in gastric mucosa. We aimed to further investigate the iodide transport in gastric mucosa and the possible role of NIS in this transport process. Iodide transport in rat gastric mucosa was studied in vitro in an Ussing chamber system using (125)I as a marker. The system allows measurements in both directions over a mucosal specimen. A considerable transport of iodide (from the serosal to the mucosal side) was established across the gastric mucosa, whereas in the opposite direction (mucosa to serosa), iodide transport was negligible. Sodium perchlorate (NaClO(4)), a competitive inhibitor of NIS, and ouabain, an inhibitor of the Na(+)/K(+)-ATPase, both attenuated gastric iodide transport from the serosal to the mucosal side. To investigate a possible neuroendocrine regulation of the iodide transport identified to occur from the serosal to the mucosal side of the stomach, thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH), vasoactive intestinal peptide (VIP), histamine, or nitric oxide donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) was added. None of these substances influenced the iodide transport. We conclude that iodide is actively transported into the gastric lumen and that this transport is at least partly mediated by NIS. Additional investigations are needed to understand the regulation and significance of this transport.     

Gastric submucosal microdialysis: a method to study gastrin- and food-evoked mobilization of ECL-cell histamine in conscious rats

Rat stomach ECL cells are rich in histamine and chromogranin A-derived peptides, such as pancreastatin. Gastrin causes the parietal cells to secrete acid by flooding them with histamine from the ECL cells. In the past, gastric histamine release has been studied using anaesthetized, surgically manipulated animals or isolated gastric mucosa, glands or ECL cells. We monitored gastric histamine mobilization in intact conscious rats by subjecting them to gastric submucosal microdialysis. A microdialysis probe was implanted into the submucosa of the acid-producing part of the stomach (day 1). The rats had access to food and water or were deprived of food (48 h), starting on day 2 after implantation of the probe. On day 4, the rats received food or gastrin (intravenous infusion), and sampling of microdialysate commenced. Samples (flow rate 1.2 microl min(-1)) were collected every 20 or 60 min, and the histamine and pancreastatin concentrations were determined. The serum gastrin concentration was determined in tail vein blood. Exogenous gastrin (4-h infusion) raised microdialysate histamine and pancreastatin dose-dependently. This effect was prevented by gastrin receptor blockade (YM022). Depletion of ECL-cell histamine by alpha-fluoromethylhistidine, an irreversible inhibitor of the histamine-forming enzyme, suppressed the gastrin-evoked release of histamine but not that of pancreastatin. Fasting lowered serum gastrin and microdialysate histamine by 50%, while refeeding raised serum gastrin and microdialysate histamine and pancreastatin 3-fold. We conclude that histamine mobilized by gastrin and food intake derives from ECL cells because: 1) Histamine and pancreastatin were released concomitantly, 2) histamine mobilization following gastrin or food intake was prevented by gastrin receptor blockade, and 3) mobilization of histamine (but not pancreastatin) was abolished by alpha-fluoromethylhistidine. Hence, gastric submucosal microdialysis allows us to monitor the mobilization of ECL-cell histamine in intact conscious rats under various experimental conditions not previously accessible to study. While gastrin receptor blockade lowered post-prandial release of ECL-cell histamine by about 80%, unilateral vagotomy reduced post-prandial mobilization of ECL-cell histamine by about 50%. Hence, both gastrin and vagal excitation contribute to the post-prandial release of ECL-cell histamine.     

Studies on adenyl cyclase in Necturus gastric mucosa

Adenyl cyclase activity of Necturus gastric mucosa was determined by measuring the amount of radioactive adenosine 3′,5′-cyclic monophosphate formed from ³H-labeled adenosine triphosphate. Histamine, pentagastrin, and fluoride added in vitro significantly increased fundic adenyl cyclase activity. The dose response curves show that the affinity of pentagastrin for adenyl cyclase is greater than that of histamine, whereas the peak response to pentagastrin is less than that to histamine. Additive stimulation was not obtained when maximal doses of pentagastrin and histamine were combined. These findings suggest that gastric mucosa contains a single adenyl cyclase unit which is coupled to distinctive selectivity sites for gastrin and histamine. N-Benzyl-3-pyrrolidyl acetate methobromide (AHR-602), the muscarinic compound, caused a significant reduction in adenyl cyclase activity, indicating a different mechanism of stimulation of gastric acid secretion for cholinergic muscarinic compounds.     

Role of gastrin in the development of gastric mucosa,ECL cells and A-like cells in newborn and young rats

Histamine-producing ECL cells and ghrelin-producing A-like cells are endocrine/paracrine cell populations in the acid-producing part of the rat stomach. While the A-like cells operate independently of gastrin, the ECL cells respond to gastrin with mobilization of histamine and chromogranin A (CGA)-derived peptides, such as pancreastatin. Gastrin is often assumed to be the driving force behind the postnatal development of the gastric mucosa in general and the ECL cells in particular. We tested this assumption by examining the oxyntic mucosa (with ECL cells and A-like cells) in developing rats under the influence of YF476, a cholecystokinin-2 (CCK(2)) receptor antagonist. The drug was administered by weekly subcutaneous injections starting at birth. The body weight gain was not affected. Weaning occurred at days 15-22 in both YF476-treated and age-matched control rats. Circulating gastrin was low at birth and reached adult levels 2 weeks after birth. During and after weaning (but not before), YF476 greatly raised the serum gastrin concentration (because of abolished acid feedback inhibition of gastrin release). The weight of the stomach was unaffected by YF476 during the first 2-3 weeks after birth. From 4 to 5 weeks of age, the weight and thickness of the gastric mucosa were lower in YF476-treated rats than in controls. Pancreastatin-immunoreactive cells (i.e. all endocrine cells in the stomach) and ghrelin-immunoreactive cells (A-like cells) were few at birth and increased gradually in number until 6-8 weeks of age (control rats). At first, YF476 did not affect the development of the pancreastatin-immunoreactive cells, but a few weeks after weaning, the cells were fewer in the YF476 rats. The ECL-cell parameters (oxyntic mucosal histamine and pancreastatin concentrations, the histidine decarboxylase (HDC) activity, the HDC mRNA levels and serum pancreastatin concentration) increased slowly until weaning in both YF476-treated and control rats. From then on, there was a further increase in the ECL-cell parameters in control rats but not in YF476 rats. The postnatal development of the ghrelin cells (i.e. the A-like cells) and of the A-like cell parameters (the oxyntic mucosal ghrelin concentration and the serum ghrelin concentrations) was not affected by YF476 at any point.We conclude that gastrin affects neither the oxyntic mucosa nor the endocrine cells before weaning. After weaning, CCK(2) receptor blockade is associated with a somewhat impaired development of the oxyntic mucosa and the ECL cells. While gastrin stimulation is of crucial importance for the onset of acid secretion during weaning and for the activation of ECL-cell histamine formation and secretion, the mucosal and ECL-cell growth at this stage is only partly gastrin-dependent. In contrast, the development of the A-like cells is independent of gastrin at all stages.