Stimulatory effects of nitric oxide donors on gastric acid secretion in isolated mouse stomach

Gastrin and Nitric Oxide Production in Cultured Gastric Antral Mucosa Are Altered in Response to a Gastric Digest of a Dietary Supplement

In vitro organ culture can provide insight into isolated mucosal responses to particular environmental stimuli. The objective of the present study was to investigate the impact of a prolonged culturing time as well as the addition of acidic gastric fluid into the in vitro environment of cultured gastric antral tissue to evaluate how altering the commonly used neutral environment impacted tissue. Furthermore, we aimed to investigate the impact of G's Formula, a dietary supplement for horses, on the secretion of gastrin, interleukin1-beta (IL-1β), and nitric oxide (NO). These biomarkers are of interest due to their effects on gastric motility and mucosal activity. Gastric mucosal tissue explants from porcine stomachs were cultured in the presence of a simulated gastric fluid (BL, n = 14), simulated gastric fluid containing the dietary supplement G's Formula (DF, n = 12), or an equal volume of phosphate buffered saline (CO, n = 14). At 48 and 60 h, 10⁻⁵ M carbachol was used to stimulate gastrin secretion. Cell viability was assessed at 72 h using calcein and ethidium-homodimer 1 staining. Media was analyzed for gastrin, IL-1β, and NO at 48, 60, and 72 h. There were no effects of treatment or carbachol stimulation on explant cell viability. Carbachol resulted in a significant increase in gastrin concentration in CO and DF treatments, but not in BL. NO was higher in CO than in BL, and NO increased in the CO and DF treatments but not in BL. In conclusion, the addition of carbachol and gastric digests to culture media did not impact cell viability. The use of an acidic gastric digest (BL) reduced the effect of cholinergic stimulation with carbachol at a concentration of 10⁻⁵ M and reduced NO secretion. The addition of the dietary supplement to the gastric digest (DF) appeared to mediate these effects within this model. Further research is required to evaluate the specific effects of this dietary supplement on direct markers of mucosal activity and the functional relevance of these results in vivo.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Dual role of nitric oxide in gastric hypersecretion in the distended stomach: inhibition of acid secretion and stimulation of pepsinongen secretion

AIMS

We investigate the role of nitric oxide (NO) in the hypersecretion of acid and pepsinogen induced by stomach distension.

MAIN METHOD

The rat stomach was distended by instillation of saline through an acute fistula under urethane anesthesia.

KEY FINDINGS

Both secretions of acid and pepsinogen were increased by the distension depending on the volume of saline introduced, and responses were attenuated by bilateral cervical vagotomy or prior administration of atropine. N(G)-nitro-l-arginine methyl ester (L-NAME) had a dual effect on these responses, causing an increase in the acid response and a decrease in the pepsin response, both in an l-arginine-sensitive manner. Distension of the stomach increased the luminal NO release; this response was suppressed by vagotomy and L-NAME. Intragastric application of FK409, a NO donor, dose-dependently increased pepsinogen secretion while decreasing acid secretion in the stomach without distension. However, serosal application of both FK409 and 8-bromo-guanosine cyclic 3', 5'-monophosphate (8-Br-cGMP) stimulated the secretion of pepsinogen in isolated mouse stomachs in vitro. The stimulatory effect of FK409 on pepsinogen secretion was totally abolished by LY83583, a guanylate cyclase inhibitor.

SIGNIFICANCE

Distension of the stomach increases both acid and pepsinogen secretion through a vagal-cholinergic pathway in addition to the luminal release of NO, and NO affects these responses in opposite ways, suppressing the acid response while enhancing the pepsin response, both mediated by a guanylate cyclase/cGMP pathway.

Direct effects of nitric oxide on histamine release from rat enterochromaffin-like cells

The direct effects of nitric oxide (NO) on enterochromaffin-like (ECL) cells have not yet been demonstrated. In this study we investigated the direct effects of NO donors on rat ECL cells. The NO donor, NOR3 (10 and 100 microM), decreased gastrin-induced histamine release. 100 microM NOR3 increased cGMP levels and reduced gastrin-induced calcium influx. ODQ, an inhibitor of guanylate cyclase, completely blocked NOR3-induced inhibition of histamine release. These results suggest that NO inhibits gastric acid secretion via suppression of gastrin-induced histamine release through a pathway in which NO activates guanylate cyclase, in addition to increasing cGMP levels and reducing gastrin-induced calcium influx. The use of NO as a new type of gastric acid inhibitor that decreases histamine levels in the stomach would be beneficial as increased histamine levels resulting from use of a histamine H2 receptor antagonist or proton pump inhibitor have various effects on tumors and immunological functions.

Nitric oxide inhibits gastric acid secretion by increasing intraparietal cell levels of cGMP in isolated human gastric glands

We have previously identified cells containing the enzyme nitric oxide (NO) synthase (NOS) in the human gastric mucosa. Moreover, we have demonstrated that endogenous and exogenous NO has been shown to decrease histamine-stimulated acid secretion in isolated human gastric glands. The present investigation aimed to further determine whether this action of NO was mediated by the activation of guanylyl cyclase (GC) and subsequent production of cGMP. Isolated gastric glands were obtained after enzymatic digestion of biopsies taken from the oxyntic mucosa of healthy volunteers. Acid secretion was assessed by measuring [(14)C]aminopyrine accumulation, and the concentration of cGMP was determined by radioimmunoassay. In addition, immunohistochemistry was used to examine the localization of cGMP in mucosal preparations after stimulation with the NO donor S-nitroso-N-acetylpenicillamine (SNAP). SNAP (0.1 mM) was shown to decrease acid secretion stimulated by histamine (50 microM); this effect was accompanied by an increase in cGMP production, which was histologically localized to parietal cells. The membrane-permeable cGMP analog dibuturyl-cGMP (db-cGMP; 0.1-1 mM) dose dependently inhibited acid secretion. Additionally, the effect of SNAP was prevented by preincubating the glands with the GC inhibitor 4H-8-bromo-1,2,4-oxadiazolo[3,4-d]benz[b][1,4]oxazin-1-one (10 microM). We therefore suggest that NO in the human gastric mucosa is of physiological importance in regulating acid secretion. Furthermore, the results show that NO-induced inhibition of gastric acid secretion is a cGMP-dependent mechanism in the parietal cell involving the activation of GC.

Stimulatory effects of endogenous and exogenous nitric oxide on gastric acid secretion in anesthetized rats

We previously reported the stimulatory effect of endogenous nitric oxide (NO) on gastric acid secretion in the isolated mouse whole stomach and histamine release from gastric histamine-containing cells. In the present study, we investigated the effects of endogenous and exogenous NO on gastric acid secretion in urethane-anesthetized rats. Acid secretion was studied in gastric-cannulated rats stimulated with several secretagogues under urethane anesthesia. The acid secretory response to the muscarinic receptor agonist bethanechol (2 mg/kg, s.c.), the cholecystokinin(2) receptor agonist pentagastrin (20 microg/kg, s.c.) or the centrally acting secretagogue 2-deoxy-D-glucose (200 mg/kg, i.v.) was dose-dependently inhibited by the NO synthase inhibitor N(omega)-nitro-L-arginine (L-NNA, 10 or 50 mg/kg, i.v.). This inhibitory effect of L-NNA was reversed by a substrate of NO synthase, L-arginine (200 mg/kg, i.v.), but not by D-arginine. The histamine H(2) receptor antagonist famotidine (1 mg/kg, i.v.) completely inhibited the acid secretory response to bethanechol, pentagastrin or 2-deoxy-D-glucose, showing that all of these secretagogues induced gastric acid secretion mainly through histamine release from gastric enterochromaffin-like cells (ECL cells). On the other hand, histamine (10 mg/kg, s.c.)-induced gastric acid secretion was not inhibited by pretreatment with L-NNA. The NO donor sodium nitroprusside (0.3-3 mg/kg, i.v.) also dose-dependently induced an increase in acid secretion. The sodium nitroprusside-induced gastric acid secretion was significantly inhibited by famotidine or by the soluble guanylate cyclase inhibitor methylene blue (50 mg/kg, i.v.). These results suggest that NO is involved in the gastric acid secretion mediated by histamine release from gastric ECL cells.

Achlorhydria by ezrin knockdown: defects in the formation/expansion of apical canaliculi in gastric parietal cells

Loss of gastric acid secretion is pathologically known as achlorhydria. Acid-secreting parietal cells are characterized by abundant expression of ezrin (Vil2), one of ezrin/radixin/moesin proteins, which generally cross-link actin filaments with plasma membrane proteins. Here, we show the direct in vivo involvement of ezrin in gastric acid secretion. Ezrin knockout (Vil2^−/−) mice did not survive >1.5 wk after birth, making difficult to examine gastric acid secretion. We then generated ezrin knockdown (Vil2^kd/kd) mice by introducing a neomycin resistance cassette between exons 2 and 3. Vil2^kd/kd mice born at the expected Mendelian ratio exhibited growth retardation and a high mortality. Approximately 7% of Vil2^kd/kd mice survived to adulthood. Ezrin protein levels in Vil2^kd/kd stomachs decreased to <5% of the wild-type levels without compensatory up-regulation of radixin or moesin. Adult Vil2^kd/kd mice suffered from severe achlorhydria. Immunofluorescence and electron microscopy revealed that this achlorhydria was caused by defects in the formation/expansion of canalicular apical membranes in gastric parietal cells.

Nitric oxide-an endogenous inhibitor of gastric acid secretion in isolated human gastric glands

BACKGROUND

Endothelial nitric oxide synthase (eNOS) has previously been detected in the glandular part of the human gastric mucosa. Furthermore, nitric oxide (NO) has been shown to influence gastric secretion in various animal models. The present study was conducted to investigate the influence of exogenously and endogenously derived NO on histamine- and cAMP-stimulated gastric acid secretion in isolated human oxyntic glands.

METHODS

Oxyntic glands were isolated from human gastric biopsies and were subsequently pre-treated with NO donors and nitric oxide synthase inhibitors and then exposed to histamine or dibutyryl-cAMP (db-cAMP). The secretory response of the glands was determined as accumulation of [14C]aminopyrine.

RESULTS

The histamine- or db-cAMP-induced acid secretion was attenuated by L-arginine, a known source of endogenous NO, and also by the NO-donors sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP). Pre-treatment with either of the NOS inhibitors NG-nitro-L-arginine methyl ester (L-NAME) or NG-nitro-L-arginine (L-NNA) enhanced the secretory response.

CONCLUSION

Our results show that NO inhibits gastric acid secretion in isolated human gastric glands, and that there is endogenous formation of NO within the glandular epithelium in the vicinity of the parietal cells.

Stimulatory effects of nitric oxide donors on histamine release in isolated rat gastric mucosal cells

We previously reported stimulatory effects of endogenous and exogenous nitric oxide (NO) on gastric acid secretion. In the present study, we investigated effects of NO donors on release of histamine, which is related to acid secretion, in isolated rat gastric mucosal cells. NO donors such as (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexanamide (NOR 1) and sodium nitroprusside significantly augmented the histamine release. It was inhibited by 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-amide (carboxy-PTIO), a NO scavenger, and 6-(phenylamino)-5,8-quinolinedione (LY83583), a soluble guanylate cyclase inhibitor. Dibutyryl cyclic GMP also stimulated histamine release. These results suggest that NO donors act on cyclic GMP pathway in isolated gastric mucosal cells, resulting in facilitation of histamine release. NO may stimulate gastric acid secretion through histamine release from the histamine-containing cells, possibly enterochromaffin-like cells.

Gastric secretion

Overlapping neural, hormonal, and paracrine pathways finely regulate gastric acid secretion. In rats and guinea pigs, most of the intrinsic neural innervation to the gastric mucosa originates in the myenteric plexus. In contrast, human stomachs have a clearly defined submucosal plexus that contains a variety of transmitters including nitric oxide, vasoactive intestinal peptide (VIP), gastrin-releasing peptide (GRP), substance P, and calcitonin gene-related peptide (CGRP). Although GRP is known to participate in meal-stimulated acid secretion by releasing gastrin in a variety of laboratory animals, recent studies were unable to demonstrate a role for endogenous GRP in meal-stimulated gastrin secretion in humans. Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the secretin-glucagon-VIP family, has been localized to gastric mucosal neurons and may participate in vagally mediated acid secretion. Two novel peptides, ghrelin and leptin, have been localized to the stomach. Peripheral administration of ghrelin stimulates and of leptin inhibits acid secretion. The binding of secretagogues to parietal cells generates changes in second messengers that regulate the translocation and activation of the proton pump, HK-ATPase. In resting cells, HK-ATPase is contained within cytoplasmic tubulovesicles in an inactive form. At stimulation, the tubulovesicles fuse with the apical canaliculi and the HK-ATPase is incorporated into the apical membrane where it actively pumps H ions in exchange for K. Acute infection with Helicobacter pylori results in hypochlorhydria, whereas chronic infection can cause either hypo- or hyperchlorhydria, depending on the distribution of the infection and the degree of corpus gastritis. Recent studies suggest that inflammatory cytokines, produced in response to the organism, can play a role in the perturbations in acid and gastrin secretion induced by H. pylori.

Antisecretory effect of somatostatin on gastric acid via inhibition of histamine release in isolated mouse stomach

Somatostatin is known to inhibit gastric acid secretion via both inhibition of histamine release from gastric enterochromaffin-like cells and direct inhibition of parietal cell function. We tried to clarify which of these two mechanisms plays a more important role in the inhibition of gastric acid section by somatostatin using isolated mouse stomach preparations. The gastric acid secretion stimulated by histamine was not inhibited by pretreatment with somatostatin (1 micro M), but somatostatin abolished acid secretion induced by 4-[[[(3-chlorophenyl)amino]carbonyl]oxy]-N,N,N,-trimethyl-2-butynyl-1-aminium chloride (McN-A-343), a muscarinic M(1) receptor agonist. In addition, the histamine-H(2) receptor antagonist famotidine also completely inhibited the secretion stimulated by McN-A-343. Similarly, pretreatment with both somatostatin and famotidine completely abolished pentagastrin-induced acid secretion. Somatostatin partially inhibited the acid secretion stimulated by bethanechol. The late sustained acid secretion induced by bethanechol was reduced more strongly by somatostatin than the initial peak secretion. In addition, somatostatin had no effect on the transient increase in bethanechol-induced acid secretion in famotidine-pretreated preparations. Somatostatin had no effect on basal histamine secretion in isolated mouse stomach preparations, but markedly reduced histamine release induced by McN-A-343 and bethanechol. The present study showed that the acid secretory response via the endogenous histamine-mediated pathway was inhibited by somatostatin, but the response to a direct activation of gastric parietal cells was not. These results suggest that the inhibition of histamine release from enterochromaffin-like cells plays a more important role in the inhibition of gastric acid secretion by somatostatin than the direct inhibition of parietal cells. In addition, somatostatin inhibited the sustained acid secretion more strongly than the initial peak secretion after the cholinergic stimulation.

Stimulatory effects of centrally injected nitric oxide donors on gastric acid secretion in anesthetized rats

The effects of centrally injected nitric oxide (NO) donors on gastric acid secretion were investigated in continuously perfused stomach of anesthetized rats. The lateral cerebroventricular (LV) injection of NOC5 (30 - 100 microg) and NOC12 (10 - 100 microg) dose-dependently stimulated gastric acid secretion. The LV injection of NOC18 (30 microg) also stimulated gastric acid secretion. The other type of NO donor, sodium nitroprusside (3 - 30 microg, LV), also dose-dependently stimulated gastric acid secretion. The effect of NOC5 at 100 microg was blocked by carboxy-PTIO, an NO scavenger, and by cervical vagotomy. Furthermore, NOC12 (30, 100 microg) dose-dependently stimulated gastric acid secretion in pylorus-ligated conscious rats. These results suggest that centrally injected NO donors stimulate gastric acid secretion in both conscious and anesthetized rats through vagus activation.