PACAP stimulates gastric acid secretion in the rat by inducing histamine release.
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Previous studies have shown that pituitary adenylate cyclase-activating peptide (PACAP) stimulates enterochromaffin-like (ECL) cell histamine release, but its role in the regulation of gastric acid secretion is disputed. This work examines the effect of PACAP-38 on aminopyrine uptake in enriched rat parietal cells and on histamine release and acid secretion in the isolated vascularly perfused rat stomach and the role of PACAP in vagally (2-deoxyglucose) stimulated acid secretion in the awake rat. PACAP has no direct effect on the isolated parietal cell as assessed by aminopyrine uptake. PACAP induces a concentration-dependent histamine release and acid secretion in the isolated stomach, and its effect on histamine release is additive to gastrin. The histamine H2 antagonist ranitidine potently inhibits PACAP-stimulated acid secretion without affecting histamine release. Vagally stimulated acid secretion is partially inhibited by a PACAP antagonist. The results from the present study strongly suggest that PACAP plays an important role in the neurohumoral regulation of gastric acid secretion. Its effect seems to be mediated by the release of ECL cell histamine. (+info)
Functional role of protein kinase B/Akt in gastric acid secretion.
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Epidermal growth factor (EGF) stimulates gastric acid secretion and H(+)/K(+)-ATPase alpha-subunit gene expression. Because EGF activates the serine-threonine protein kinase Akt, we explored the role of Akt in gastric acid secretion. Akt phosphorylation and activation were measured by kinase assays and by Western blots with an anti-phospho-Akt antibody, using lysates of purified (>95%) canine gastric parietal cells in primary culture. EGF induced Akt phosphorylation and activation, whereas carbachol had no effect. LY294002, an inhibitor of phosphoinositide 3-kinase, completely blocked EGF induction of Akt phosphorylation, whereas the MEK1 inhibitor PD98059 and the protein kinase C inhibitor GF109203X had no effect. We examined the role of Akt in H(+)/K(+)-ATPase gene expression by Northern blotting using a canine H(+)/K(+)-ATPase alpha-subunit cDNA probe. The parietal cells were transduced with a multiplicity of infection of 100 of the adenoviral vector Ad.Myr-Akt, which overexpresses a constitutively active Akt gene, or with the control vector Ad.CMV-beta-gal, which expresses beta-galactosidase. Ad.Myr-Akt induced H(+)/K(+)-ATPase alpha-subunit gene expression 3-fold, whereas it failed to stimulate the gene cyclooxygenase-2, which was potently induced by carbachol in the same parietal cells. Ad.Myr-Akt induced aminopyrine uptake 4-fold, and it potentiated the stimulatory action of carbachol 3-fold. In contrast, Ad.Myr-Akt failed to induce changes in either parietal cell actin content, measured by Western blots with an anti-actin antibody or in the organization of the actin cellular cytoskeleton, visualized by fluorescein phalloidin staining and confocal microscopy. Transduction of the parietal cells with a multiplicity of infection of 100 of the adenoviral vector Ad.dom.neg.Akt, which overexpresses an inhibitor of Akt, blocked the stimulatory effect of EGF on both aminopyrine uptake and H(+)/K(+)-ATPase production, measured by Western blots with an anti-H(+)/K(+)-ATPase alpha-subunit antibody. Thus, EGF induces a cascade of events in the parietal cells that results in the activation of Akt. The functional role of Akt appears to be stimulation of gastric acid secretion through induction of H(+)/K(+)-ATPase expression. (+info)
Beta-cell, thyroid, gastric, adrenal and coeliac autoimmunity and HLA-DQ types in type 1 diabetes.
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The autoimmune attack in type 1 diabetes is not only targeted to beta cells. We assessed the prevalence of thyroid peroxidase (aTPO), parietal cell (PCA), antiadrenal (AAA) and endomysial antibodies (EmA-IgA), and of overt autoimmune disease in type 1 diabetes, in relation to gender, age, duration of disease, age at onset, beta-cell antibody status (ICA, GADA, IA2A) and HLA-DQ type. Sera from 399 type 1 diabetic patients (M/F: 188/211; mean age: 26 +/- 16 years; duration: 9 +/- 8 years) were tested for ICA, PCA, AAA and EmA-IgA by indirect immunofluorescence, and for IA2A (tyrosine phosphatase antibodies), GADA (glutamic acid decarboxylase-65 antibodies) and aTPO by radiobinding assays. The prevalence rates were: GADA 70%; IA2A, 44%; ICA, 39%; aTPO, 22%; PCA, 18%; EmA-IgA, 2%; and AAA, 1%. aTPO status was determined by female gender (beta = - 1.15, P = 0.002), age (beta = 0.02, P = 0.01) and GADA + (beta = 1.06, P = 0.02), but not by HLA-DQ type or IA2A status. Dysthyroidism (P < 0.0001) was more frequent in aTPO + subjects. PCA status was determined by age (beta = 0.03, P = 0.002). We also observed an association between PCA + and GADA + (OR = 1.9, P = 0.049), aTPO + (OR = 1.9, P = 0.04) and HLA DQA1*0501-DQB1*0301 status (OR = 2.4, P = 0.045). Iron deficiency anaemia (OR = 3.0, P = 0.003) and pernicious anaemia (OR = 40, P < 0.0001) were more frequent in PCA + subjects. EmA-IgA + was linked to HLA DQA1*0501-DQB1*0201 + (OR = 7.5, P = 0.039), and coeliac disease was found in three patients. No patient had Addison's disease. In conclusion, GADA but not IA2A indicate the presence of thyrogastric autoimmunity in type 1 diabetes. aTPO have a female preponderance, PCA are weakly associated with HLA DQA1*0501-DQB1*0301 and EmA-IgA + with HLA DQA1*0501-DQB1*0201. (+info)
Regulation of gastric epithelial cell development revealed in H(+)/K(+)-ATPase beta-subunit- and gastrin-deficient mice.
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The gastric H(+)/K(+)-ATPase is essential for normal development of parietal cells. Here we have directly assessed the role of the H(+)/K(+)-ATPase beta-subunit (H/K-beta) on epithelial cell development by detailed quantitation of the epithelial cell types of the gastric mucosa of H/K-beta-deficient mice. H/K-beta-deficient mice had a 3.1-fold increase in the number of immature cells per gastric unit; however, the numbers of surface mucous and parietal cells were similar to those in the gastric units of wild-type mice. The effect of elevated gastrin levels in the H/K-beta-deficient mice was determined by producing mice that are also deficient in gastrin. We demonstrated that the increased production of immature cells and resulting hypertrophy is caused by the overproduction of gastrin. However, the depletion of zymogenic cells, which is another feature of H/K-beta-deficient mice, is independent of hypergastrinemia. Significantly, parietal cells of H/K-beta- and gastrin-deficient mice had abnormal secretory membranes and were devoid of resting tubulovesicular membranes. Together these data suggest a homeostatic mechanism limiting the number of immature cells that can develop into end-stage epithelial cells and indicate a direct role for H/K-beta in the development of mature parietal cells. (+info)
A molecular profile of the mouse gastric parietal cell with and without exposure to Helicobacter pylori.
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The parietal cell (PC) plays an important role in normal gastric physiology and in common diseases of the stomach. Although the genes involved in acid secretion are well known, there is limited molecular information about other aspects of PC function. We have generated a comprehensive database of genes expressed preferentially in PCs relative to other gastric mucosal cell lineages. PCs were purified from FVB/N mouse stomachs by lectin panning. cRNA generated from PC-enriched (PC(+)) and PC-depleted (PC(-)) populations were used to query oligonucleotide-based microarrays. False-positive signals were filtered by using a new algorithm for noise reduction and selected results independently audited by real-time quantitative reverse transcription (RT)-PCR. The annotated database of 240 genes reveals previously unappreciated aspects of cellular function, including factors that may mediate PC regulation of gastric stem cell proliferation. PC(+) and PC(-) expression profiles were also prepared from germ-free mice 2 and 8 weeks after colonization with a clinical isolate of Helicobacter pylori (Hp)--the pathogen that produces acid-peptic disease (gastritis, ulcers) in humans. Whereas PC(+) gene expression was remarkably constant, the PC(-) fractions demonstrated a robust, evolving host response, with increased expression of genes involved in cell motility/migration, extracellular matrix interactions, and IFN responses. The consistency of PC(+) gene expression allowed identification of a cohort of 92 genes enriched in PCs under all conditions studied. These genes provide a molecular profile that can be used to define this epithelial lineage under a variety of physiologic, pharmacologic, and pathologic stimuli. (+info)
Simultaneous measurement and imaging of intracellular Ca(2+) and H(+) transport in isolated rabbit gastric glands.
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1. Activation of H(+) secretion in the intracellular canaliculi of parietal cells occurs on an unknown time scale with ill-defined kinetics for the coupling of H(+) secretion and the elevation of intracellular calcium ([Ca(2+)](i)) stimulated by secretagogues. 2. We developed a method to determine H(+) secretion in isolated rabbit gastric glands with spatio-temporal resolution, using the fluorescent indicator Lysosensor Yellow-Blue (LYB). Glands accumulated the dye exclusively in the intracellular canaliculi of parietal cells and the gland lumen. Dye fluorescence in the acid spaces of the glands increased upon stimulation of acid secretion by carbachol, histamine and forskolin. Simultaneous fluorescence measurements of acid secretion and [Ca(2+)](i) at 1 s resolution were made by joint loading of LYB and Fluo-3. 3. Carbachol-stimulated H(+) secretion was detected in the gland lumen as early as 3 s after the onset of the [Ca(2+)](i) spike. H(+) accumulation appeared to be transient and paralleled the release component of the [Ca(2+)](i) spike. Short and repetitive stimulations with carbachol elicited repetitive responses in [Ca(2+)](i) and H(+) secretion. 4. Histamine or forskolin stimulated H(+) secretion with a delayed onset (around 2 min) and a sustained response. Acid secretion was temporally unrelated to the oscillatory Ca(2+) responses. 5. The striking difference in the kinetics of activation of H(+) secretion by cholinergic and cAMP-dependent secretagogues indicates that two distinct mechanisms are operating in the final stimulation of the pump, in spite of both eliciting a [Ca(2+)](i) response. (+info)
Hypergastrinemia in response to gastric inflammation suppresses somatostatin.
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Hypergastrinemia and a reduction in tissue somatostatin occur in Helicobacter pylori-infected patients. We investigated whether the D cell may be a direct target of gastric inflammation and hypergastrinemia. D cells were quantified by morphometry and flow cytometry in 16-wk-old wild-type (G+/+) and gastrin-deficient (G-/-) mice. Hypochlorhydric G-/- mice were treated with either antibiotics for 20 days or infused with gastrin (G-17) for 14 days. G+/+ mice were made hypochlorhydric by treating them with omeprazole for 2 mo. G-/- mice showed significant inflammation compared with the G+/+ mice, which resolved after 20 days of antibiotic treatment. D cell numbers were not significantly different between G-/- and G+/+ mice. After G-17 was infused, fundic and antral D cell numbers decreased in the G-/- mice. G+/+ animals made hypergastrinemic with omeprazole exhibited decreased D cell numbers. When omeprazole-treated mice were treated with antibiotics alone, elevated plasma gastrin levels returned to baseline and D cell numbers returned to resting levels despite persistent hypochlorhydria. Hypergastrinemia, induced by inflammation, results in decreased D cell numbers. Thus the stomach responds to the presence of inflammation by reducing somatostatin levels, thereby releasing the inhibition on the G and parietal cells to maximize gastric acid output. (+info)
Pharmacological regulation of gastric acid secretion in the apical membrane of parietal cells; a new target for antisecretory drugs.
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We examined the local effect of several drugs against secretagogue-stimulated acid secretion in dogs. Test drugs were applied to denervated gastric pouches in conscious dogs either for 5 to 30 min beginning 1 hr after or for 30 min before intravenous infusion of gastric secretagogues (histamine, pentagastrin, or carbachol). The antisecretory effect of test drugs delivered by an intravenous or oral route was also examined. Local application of acid pump inhibitors (omeprazole, leminoprazole) for 30 min beginning 1 hr after histamine infusion significantly inhibited gastric acid secretion. The effect of leminoprazole persisted for more than 8 hr after a 30 min application. A mast cell stabilizer (FPL 52694) applied to pouches for 15 to 30 min also potently inhibited histamine-stimulated gastric acid secretion in a time-dependent manner. The duration of the antisecretory effect of such drugs after a 30 min application was greater than 4 hr. Locally applied leminoprazole and FPL 52694 for 30 min also significantly inhibited pentagastrin- and carbachol-stimulated gastric acid secretion. Although intravenous omeprazole and leminoprazole exerted a potent antisecretory effect on histamine-induced acid secretion FPL 52694 had little or no antisecretory effect following intravenous or oral administration. 16,16-dimethyl prostagladin E2 also locally inhibited histamine-stimulated acid secretion. Acid stable local anesthetics (tetracaine, ethyl-4-aminobenzoate), histamine H2-receptor blockers (cimetidine, ranitidine, and famotidine), and a muscarinic M1-receptor antagonist (pirenzepine) did not exhibit local antisecretory effects. Such results strongly suggest that the apical membrane of parietal cells possesses a pharmcologically sensitive portion similar to the basolateral membrane, which usually mediates gastric acid secretion. The apical membrane represents an intriguing target for new antisecretory drugs, as well as a new medium for further elucidating the functional features of parietal cells. (+info)