Gastric acid response to pylorus ligation in rats: is gastrin or histamine involved?

Rivastigmine ameliorates indomethacin experimentally induced gastric mucosal injury via activating α7nAChR with inhibiting oxidative stress and apoptosis

The current study aimed to investigate the potential ameliorative role of Rivastigmine (RIVA), the anti-Alzheimer drug, against the gastric mucosal injury caused by indomethacin (IND). The rats were divided into four groups: group I was given a vehicle as a control, group II was given RIVA (0.3 mg/kg) once daily intraperitoneal (ip) for 2 weeks, group III was given a single IP dose of 30 mg/kg IND, and group IV was given RIVA ip 2 weeks before the administration of IND. The gastric mucosal injury was detected by the estimation of ulcer index, gastric acidity, pepsin, and mucin concentrations. Malondialdehyde (MDA), superoxide dismutase (SOD), reduced glutathione (GSH), total nitrite/nitrate (NOx), and the expression of tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), nuclear factor kappa B (NF-κB), Hemoxygenase 1 (HO-1), and caspase-3 were all measured in gastric tissue. In addition, histological assessment and proliferating cell nuclear antigen (PCNA) immuno-expression were studied. Gastric mucosal injury induced by IND was indicated by both biochemical and histopathological assessments. RIVA Pretreatment reduced ulcer index, MDA, TNF-α, IL-6, NF-κB, and caspase-3 and increased SOD, GSH, NOx, and HO-1. RIVA improved the suppressed nuclear immunoreaction for PCNA observed with IND. The current findings provide novel evidence that RIVA possesses a prophylactic action against IND-induced gastric mucosal damage in rats. Despite being a cholinergic drug that is associated with increased pepsin and stomach acidity, RIVA protected against IND-induced gastric mucosal injury via activating α7nAChR and inhibiting oxidative stress and apoptosis.

Gastric acid response to acute exposure to hypergravity

The influence of environmental stressors on the pathogenesis of gastrointestinal disease has received increased awareness. Stress affects different physiological functions of the gastrointestinal tract, including gastric acid secretion and mucosal blood flow. Repeated exposures of rapid-onset, highly-sustained hypergravity cause severe physical stress in the pilot. Although the effects of exposure to hypergravity on cardiovascular and cerebral functions have been the subjects of numerous studies, crucial information regarding pathophysiological changes in the gastrointestinal tract following hypergravity exposure is lacking. In this study, we investigated the effects of acute exposure to hypergravity on gastric secretory activity and gastrin release. Male Sprague-Dawley rats were exposed to +10Gz three times for 3 min. Gastric juice and blood were collected. The volume and total acidity of gastric juice, and the plasma gastrin level was measured. Acute exposure to +10Gz significantly decreased the gastric juice parameters. The gastric juice volume and total acidity of hypergravity-exposed rats were 3.54 ± 0.32 mL/100 g and 84.90 ± 5.17 mEq/L, respectively, which were significantly lower than those of the nonexposed rats (4.62 ± 0.39 mL/100 g and 97.37 ± 5.42 mEq/L; P < 0.001 and P < 0.001, respectively). In contrast, plasma gastrin level was not significantly altered following hypergravity exposure. We demonstrated that acute exposure to hypergravity led to a significant decrease in the gastric juice volume and acidity but did not alter the plasma gastrin level.

Protective effects of Weilikang decoction on gastric ulcers and possible mechanisms

Although Weilikang decoction (WLK) has been used for gastric ulcer (GU) therapy in a clinical setting with good curative effect for >20 years, the mechanism remains unclear. Several GU animal models, induced by ethanol, hydrochloric acid, aspirin, pylorus ligation, acetic acid and indomethacin, were used to investigate the gastroprotective effects of WLK decoction. Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), indomethacin, and N-ethylmaleimide (NEM) were pretreated, respectively, to investigate the action mechanism. Real-time polymerase chain reaction and Western blot analysis methods were used to determine the effects of WLK on indomethacin-induced GUs. The WLK-administered groups (2.5, 1.25 and 0.625 g/kg) significantly reduced the GU areas induced by ethanol, hydrochloric acid and aspirin. Furthermore, the effects could be quenched by L-NAME and NEM, but not by indomethacin. The 2.5 and 1.25 g/kg WLK groups showed significantly decreased effects on GU areas induced by pylorus ligation and acetic acid. WLK treatment significantly decreased mRNA expression on cyclooxygenase (COX)-1, COX-2, interleukin-6, tumor necrosis factor α and inducible nitric oxide synthase (iNOS) mRNA, but showed no effect on endothelial nitric oxide synthase mRNA expression. Western blot analysis result showed that WLK-treated groups markedly downregulated COX-2 protein expression. The anti-ulcer potential of WLK can be primarily attributed to its regulatory effects on nitric oxide, sulfhydryl compounds, and reduction effect on mucosal expression of proinflammatory cytokines.

Protective effect of hydrogen sulfide against cold restraint stress-induced gastric mucosal injury in rats

Hydrogen sulfide (H2S) is an endogenous gaseous mediator plays a potential role in modulating gastric inflammatory responses. However, its putative protective role remains to be defined. The present study aimed to evaluate role of the exogenously released and endogenously synthesized H2S in cold restraint stress (CRS)-induced oxidative gastric damage in rats. Rats were restrained, and maintained at 4 °C for 3 h. The H2S donor, sodium hydrosulfide (NaHS) (60 μmol/kg) was injected intraperitoneally (i.p.) before CRS. Our results revealed that NaHS pretreatment significantly attenuated ulcer index, free and total acid output, and pepsin activity in gastric juice along with decreased gastric mucosal carbonyl content and reactive oxygen species production. This was accompanied by increased gastric juice pH and mucin concentration in addition to restoring the deficits in the gastric reduced glutathione, catalase as well as superoxide dismutase enzyme activities. NaHS pretreatment markedly reduced the serum level of tumor necrosis factor (TNF-α) and myeloperoxidase activity compared to CRS-non-treated. Moreover, NaHS preadministration significantly abrogated the inflammatory and the deleterious responses of gastric mucosa in CRS. The protective effects of H2S were confirmed by gastric histopathological examination. However, pretreatment with the H2S-synthesizing enzyme, cystathionine-gamma-lyase inhibitor, beta-cyano-L-alanine (50 mg/kg, i.p.) reversed the gastroprotection afforded by the endogenous H2S. Collectively, our results suggest that H2S can protect rat gastric mucosa against CRS-induced gastric ulceration possibly through mechanisms that involve anti-oxidant and anti-inflammatory actions alongside enhancement of gastric mucosal barrier and reduction in acid secretory parameters.

Altered physiology of acid secretion in depression-prone Flinders rats results in exacerbated NSAID and stress-induced gastric damage

BACKGROUND

Flinders Sensitive Line (FSL) rats are characterized by hypersensitivity to cholinergic stimuli and have been extensively used for studying depressive disorders. A link between depression and peptic ulcers has long been established; however, there is a lack of data from animal models.

METHODS

We studied the physiology of acid secretion in FSL and Flinders Resistant Line (FRL) rats in vivo and in vitro. We also examined the susceptibility of Flinders rats to water immersion restraint stress (WIRS) or NSAID-induced gastric damage and explored the effect of an anticholinergic agent, atropine, in reversing this effect.

KEY RESULTS

Basal acid output was more than twofold greater in FSL compared with FRL rats in vivo, 213.5 and 92.8 μEq/3 h/100 g (P = 0.02), respectively. Carbachol was a more potent secretagog in vitro, and somatostatin was a less potent inhibitory agent, while paradoxically stimulating acid secretion over and above the carbachol response in gastric glands from FSL rats. The FSL rats were more susceptible to indomethacin and WIRS-induced gastric mucosal damage compared with FRL rats. Atropine reduced acid output, which resulted in a reduction in indomethacin and stress-induced gastric damage in FSL rats.

CONCLUSIONS & INFERENCES

Our study, for the first time, demonstrates that the altered vagally mediated physiology of acid secretion in depression-prone FSL rats contributes to gastric hypersecretion and, consequently, results in exacerbated stress and NSAID-induced gastric damage. Flinders rats may be a useful animal model for studying acid-related and also gastrointestinal functional disorders in depression.

Inhibition of endogenous CO by ZnPP protects against stress-induced gastric lesion in adult male albino rats

Carbon monoxide (CO) has been found to be produced in every living cell in a biochemical reaction catalyzed by heme-oxygenase (HO) enzyme which degrades heme into biliverdin, CO, and iron. Endogenous CO is not a waste product, but acts as a chemical messenger mediating and modulating many intracellular biochemical reactions that regulate physiological functions. This study was designed to investigate the effect of inhibition of endogenous CO production by zinc protoporphyrin (ZnPP), an HO inhibitor, on the gastric secretion and ulceration induced by cold-restraint stress (CRS) in adult male albino rats. Rats were pylorically ligated and divided randomly into the following groups (six rats each): control, ZnPP treated (50 μmol/kg/day, s.c. for 10 days), CRS, and stressed ZnPP treated groups. Blood samples were collected from the retro-orbital sinus of anesthetized rats for determination of CO concentration. We found that ZnPP pretreatment significantly decreased HO-1 level, CO level, and volume of gastric juice as compared to the control non-stressed rats. In the present study, ZnPP pretreatment proved to be protective against development of ulcerative lesions in CRS model as evidenced by reduction of the ulcer index, and this could be mediated through reduction of free and total acidity of gastric secretion and decreased lipid peroxidation but with significantly decreased gastric protective nitric oxide and prostaglandin E(2) levels. In conclusion and according to our results, the protective effect of ZnPP on CRS-induced gastric ulcers despite of inhibition of endogenous CO could be attributed to the presence of zinc which is known to have a protective anti-ulcer effect.

Ameliorative effects of telmisartan in diabetic rats with indomethacin-induced gastric ulceration

The protective effects of telmisartan, the angiotensin II-receptor antagonist, were investigated in rats with type 2 diabetes mellitus exposed to acute gastric ulceration. Following successful induction of diabetes, telmisartan treatment (1 mg/kg/day, orally) was started and continued for 8 weeks, after which acute gastric ulceration was induced by indomethacin. Telmisartan significantly attenuated the hyperglycemia and hypoinsulinemia in diabetic rats. Also, telmisartan significantly reduced the elevations of total gastric acid output, pepsin activity, gastric ulcer index and gastric mucosal tumor necrosis factor-alpha, nitric oxide, malondialdehyde and caspase-3 activity, and restored the depleted antioxidant defenses (reduced glutathione level, and superoxide dismutase and catalase activities) caused by indomethacin administration in diabetic rats. Histopathological gastric tissue damage induced by indomethacin in diabetic rats was ameliorated by telmisartan treatment. Immunohistochemical analysis revealed that telmisartan markedly attenuated the reduction in insulin content of pancreatic islet beta-cells, and prevented the indomethacin-induced overexpression of inducible nitric oxide synthase and nuclear factor-kappaB in gastric mucosa of diabetic rats. It was concluded that telmisartan represents a potential therapeutic option to reduce the risk of gastric ulceration induced by nonsteroidal anti-inflammatory drugs in type 2 diabetic patients.

Gastroprotective effect of simvastatin against indomethacin-induced gastric ulcer in rats: role of nitric oxide and prostaglandins

This study investigated the possible mechanisms underlying the gastroprotective effect of simvastatin against indomethacin-induced gastric ulcer in rats. Rats were randomly assigned to vehicle-, simvastatin-, simvastatin+L-arginine- and simvastatin+N(G)-nitro-L-arginine methyl ester (L-NAME)-pretreated groups for two weeks. Pyloric ligation was performed for the collection of gastric juice, and gastric ulceration was induced by a single intraperitoneal injection of indomethacin (30 mg/kg). Gastric juice parameters (total acid output, pepsin activity and mucin concentration) were determined. The stomachs tissues were used for determination of gastric mucosal lipid peroxides, superoxide dismutase, catalase, total nitrites and prostaglandin E(2) levels. Pretreatment with simvastatin (10 mg/kg, orally, for 2 weeks) caused significant reduction in gastric mucosal lesions and lipid peroxides associated with a significant increase in gastric juice mucin concentration. Simvastatin significantly increased the gastric mucosal total nitrite and prostaglandin E(2) levels. Additionally, simvastatin attenuated the elevations in gastric mucosal superoxide dismutase observed with indomethacin. The gastroprotective effect afforded by simvastatin was significantly augmented by coadministration with L-arginine (a nitric oxide precursor) and inhibited by coadministration with L-NAME (a nitric oxide synthase inhibitor). Results confirm a gastroprotective effect for simvastatin, and indicate that the anti-ulcer effect of simvastatin is mediated by scavenging free radicals, increasing nitric oxide and prostaglandin E(2) levels, and increasing gastric juice mucin production. We conclude that simvastatin represents a more suitable antihyperlipidemic therapy for patients who are at risk of gastric ulcers that were induced by the use of nonsteroidal anti-inflammatory drugs (NSAIDs).

Role of Na-K-2Cl cotransporter-1 in gastric secretion of nonacidic fluid and pepsinogen

Na-K-2Cl cotransporter-1 (NKCC) has been detected at exceptionally high levels in the gastric mucosa of several species, prompting speculation that it plays important roles in gastric secretion. To investigate this possibility, we 1) immunolocalized NKCC protein in the mouse gastric mucosa, 2) compared the volume and composition of gastric fluid from NKCC-deficient mice and their normal littermates, and 3) measured acid secretion and electrogenic ion transport by chambered mouse gastric mucosa. NKCC was localized to the basolateral margin of parietal cells, mucous neck cells, and antral base cells. In NKCC-deficient mice, gastric secretions of Na+, K+, Cl-, fluid, and pepsinogen were markedly impaired, whereas secretion of acid was normal. After stimulation with forskolin or 8-bromo-cAMP, chambered corpus mucosa vigorously secreted acid, and this was accompanied by an increase in transmucosal electrical current. Inhibition of NKCC with bumetanide reduced current to resting levels but had no effect on acid output. Although prominent pathways for basolateral Cl- uptake (NKCC) and apical Cl- exit [cystic fibrosis transmembrane conductance regulator (CFTR)] were found in antral base cells, no impairment in gastric secretion was detected in CFTR-deficient mice. Our results establish that NKCC contributes importantly to secretions of Na+, K+, Cl-, fluid, and pepsinogen by the gastric mucosa through a process that is electrogenic in character and independent of acid secretion. The probable source of the NKCC-dependent nonacidic electrogenic fluid secretion is the parietal cell. The observed dependence of pepsinogen secretion on NKCC supports the concept that a nonacidic secretory stream elaborated from parietal cells facilitates flushing of the proenzyme from the gastric gland lumen.

The vagus regulates histamine mobilization from rat stomach ECL cells by controlling their sensitivity to gastrin

The ECL cells in the oxyntic mucosa secrete histamine in response to gastrin, stimulating parietal cells to produce acid. Do they also operate under nervous control? The present study examines histamine mobilization from rat stomach ECL cells in situ in response to acute vagal excitation and to food or gastrin following vagal or sympathetic denervation. Applying the technique of microdialysis, we monitored the release of histamine by radioimmunoassay. Microdialysis probes were placed in the submucosa on either side of the stomach, 3 days before experiments. The rats were awake during microdialysis except when subjected to electrical vagal stimulation. One-sided electrical vagal stimulation raised serum gastrin and mobilized gastric histamine. However, gastrin receptor blockade prevented the histamine mobilization, indicating that circulating gastrin accounts for the response. Vagal excitation by hypoglycaemia (insulin) or pylorus ligation did not mobilize either gastrin or histamine. The histamine response to food was almost abolished by gastrin receptor blockade, and it was halved on the denervated side after unilateral subdiaphragmatic vagotomy. While the histamine response to a near-maximally effective dose of gastrin was unaffected by vagotomy, the response to low gastrin doses was reduced significantly. Abdominal ganglionic sympathectomy failed to affect the histamine response to either food or gastrin. In conclusion, gastrin is responsible for most of the food-evoked mobilization of ECL-cell histamine. The histamine response to electrical vagal stimulation reflects the effect of circulating gastrin rather than a direct action of the vagus on the ECL cells. Vagal denervation was accompanied by an impaired histamine response to food intake, probably reflecting the right-ward shift of the serum gastrin concentration-histamine response curve. The results suggest that the vagus controls the sensitivity of the ECL cells to gastrin.

Botulinum toxin in gastric submucosa reduces stimulated HCl production in rats

BACKGROUND

Botulinum toxin blocks acetylcholine release from nerve endings and acts as a long term, reversible inhibitor of muscle contraction as well as of salivary, sweat gland, adrenal and prostatic secretions. The aim of the present study is to investigate whether gastric submucosal injection of botulinum toxin type A reduces stimulated gastric production of HCl.

METHODS

Sixty-four rats were randomized in two groups and laparotomized. One group was treated with botulinum toxin-A 10 U by multiple submucosal gastric injections, while the second group was injected with saline. Two weeks later, acid secretion was stimulated by pyloric ligation and acid output was measured. Body weight, food and water intake were also recorded daily.

RESULTS

HCl production after pyloric ligation was found to be significantly lower in botulinum toxin-treated rats (657 +/- 90.25 micromol HCl vs. 1247 +/- 152. P = 0.0017). Botulinum toxin-treated rats also showed significantly lower food intake and weight gain.

CONCLUSIONS

Botulinum toxin type A reduces stimulated gastric acidity. This is likely due either to inhibition of the cholinergic stimulation of gastric parietal cells, or to an action on the myenteric nervous plexuses. Reduction of growth and food intake may reflect both impaired digestion and decreased gastric motility.

Ghrelin acts in the central nervous system to stimulate gastric acid secretion

Ghrelin is a novel acylated peptide that functions in the regulation of growth hormone release and energy metabolism. It was isolated from rat stomach as an endogenous ligand for growth hormone secretagogue receptor. Ghrelin is also localized in the arcuate nucleus of rat hypothalamus. Intracerebroventricular (ICV) administration increases food intake and body weight. We examined the effect of ghrelin on gastric acid secretion in urethane-anesthetized rats and found that ICV administration of ghrelin increased gastric acid output in a dose-dependent manner. Vagotomy and administration of atropine abolished the gastric acid secretion induced by ghrelin. ICV administration of ghrelin also induced c-fos expression in the neurons of the nucleus of the solitary tract and the dorsomotor nucleus of the vagus, which are key sites in the central nervous system for regulation of gastric acid secretion. Our results suggest that ghrelin participates in the central regulation of gastric acid secretion by activating the vagus system.

Glycine-extended gastrin synergizes with gastrin 17 to stimulate acid secretion in gastrin-deficient mice

BACKGROUND & AIMS

Studies in gastrin-deficient mice have demonstrated critical roles for gastrin peptides in the regulation of gastric acid secretion, but the relative contributions of amidated (G-17) and glycine-extended (G17-Gly) gastrin remain unclear. We examined the effects of these 2 forms of gastrin on acid secretion in gastrin-deficient mice.

METHODS

Sixty gastrin-deficient mice received infusions of saline, or 1, 6, or 14 days of amidated gastrin 17 (G-17), G17-Gly, or both G-17 and G17-Gly at 10 nmol. kg(-1). h(-1). Twenty-four gastrin-deficient mice were then infused for 14 days with 1, 2, or 5 nmol. kg(-1). h(-1) of G-17 or G-17 and G17-Gly. Acid secretion was determined 4 hours after pyloric ligation, and gastric tissue was processed for histology, immunohistochemistry, and electron microscopy.

RESULTS

Infusion of G-17 increased acid secretion in a dose-dependent manner with a peak at 5 nmol. kg(-1). h(-1) and a subsequent decrease in acid secretion at higher doses. Infusion of G17-Gly alone had no effect on acid secretion, but coinfusion with G-17 resulted in significantly higher levels of acid secretion at all doses examined than infusion with G-17 alone. The potentiating effect of G17-Gly on G-17-induced acid secretion was associated with increased parietal cell activation but was independent of changes in parietal and enterochromaffin-like cell number, fundic proliferation rates, and H(+),K(+)-adenine triphosphatase expression. G17-Gly also prevented the formation of vacuolar canaliculi and lipofuscin bodies in the parietal cells induced by G-17.

CONCLUSIONS

G17-Gly appears to synergize with G-17 to up-regulate acid secretion and prevent parietal cell degradation. These results suggest that G17-Gly plays an important role in parietal cell function.

Some aspects of the effects of PL-10.1.AK-15 on the gastrointestinal tract

PL-10.1.AK-15 is an active fragment of a naturally occurring protein first isolated from human gastric juice. Among its other protective effects, PL-10.1.AK-15 has demonstrated a protective effect on the gastrointestinal tract. The aim of this study was to investigate the influence of PL-10.1.AK-15 on two functional parameters of gastrointestinal function: gastric acid secretion and gastrointestinal motility. Gastric acid secretion was assessed in male Wistar rats using a modified method of Shay, while gastrointestinal motility was assessed in male NMRI mice by charcoal propulsion. PL-10.1.AK-15 was given in three different doses (3, 10 and 100 micrograms/kg body weight) in accordance with the experimental protocol. The results of these experiments indicate that PL-10.1.AK-15 in the investigated doses had no influence on gastric acid secretion or gastrointestinal motility.

Effect of cholecystokinin-B/gastrin receptor blockade on gastric acid secretion in conscious rats

Gastrin, histamine and acetylcholine are physiological stimuli of gastric acid secretion. The cholecystokinin-B/gastrin receptor antagonists YM022 and RP73870 were used to study the effect of gastrin receptor blockade on acid secretion. Gastrin, histamine, insulin or bethanechol were administered to conscious gastric fistula rats with or without the concomitant intravenous infusion of YM022 or RP73870. Other rats were subjected to pylorus ligation. YM022 and RP73870 inhibited the gastrin-induced acid secretion in a dose- and time-dependent manner; maximal inhibition was observed at a dose of 0.3 mumol.kg-1.hr-1 for both YM022 and RP73870, the ID50 values being 0.02 mumol.kg-1.hr-1 and 0.05 mumol.kg-1.hr-1 for YM022 and RP7870, respectively. At a dose of 0.3 mumol.kg-1.hr-1 YM022 and RP73870 failed to inhibit basal and histamine-, bethanechol-, and insulin-evoked secretion. They also failed to affect the secretion evoked by infusion of a cocktail of maximally effective doses of gastrin-17, histamine and bethanechol. YM022 and RP73870, finally, were without effect on the acid response to pylorus ligation. We suggest that endogenous gastrin in the conscious rat does not contribute to the basal acid secretion and does not participate in the acid response to histamine or to vagus stimulation.

Rat stomach enterochromaffin-like cells are not stimulated by pylorus ligation. A biochemical and ultrastructural study

BACKGROUND

The enterochromaffin-like (ECL) cells in the rat oxyntic mucosa produce histamine and contain cytoplasmic granules, microvesicles, and secretory vesicles. The cells respond to gastrin by the release of histamine (associated with loss of secretory vesicles), which is thought to mediate the gastrin-induced stimulation of the parietal cells. Gastric acid secretion is stimulated also by vagal excitation, which can be induced, for instance, by pylorus ligation. The present study addresses the question whether the ECL cells are involved in the acid response to pylorus ligation.

METHODS

Rats were subjected to pylorus ligation and killed 4 or 16 h later. Other rats were subjected to sham operation (laparotomy). Some of the rats received human Leu15-gastrin-17 (5 nmol/kg/h) by intravenous infusion for 30 or 60 min before being killed. The serum gastrin concentration, the oxyntic mucosal histidine decarboxylase (HDC) activity, HDC mRNA concentration, histamine concentration, and gastric acid output were measured. Specimens from the oxyntic mucosa were processed for transmission electron microscopy. Electron micrographs of ECL cells were analyzed planimetrically.

RESULTS

The gastric acid output was high, but the serum gastrin concentration was not affected by the pylorus ligation. The HDC activity and the level of HDC mRNA in the oxyntic mucosa were reduced, but the histamine concentration was unchanged. The secretory vesicles and granules of the ECL cells were unaffected, whereas the number and volume density of the microvesicles were reduced. Gastrin administration to sham-operated and pylorus-ligated rats lowered the oxyntic mucosal histamine concentration and increased the HDC activity in both groups.

CONCLUSIONS

ECL cells in the rat stomach do not mediate the gastric acid response to pylorus ligation, and ECL cells in the pylorus-ligated stomach retain their ability to respond to gastrin with activation.

Gastric acid secretion after depletion of enterochromaffin-like cell histamine. A study with alpha-fluoromethylhistidine in rats

BACKGROUND

Histamine is thought to play a central role in the regulation of gastric acid secretion. In the rat oxyntic mucosa most of the histamine is synthesized and stored in enterochromaffin-like (ECL) cells, and the rest resides in mast cells. The present study examines the role of ECL-cell histamine in the control of acid secretion in the intact, conscious rat.

METHODS

Rats were treated with alpha-fluoromethylhistidine (alpha-FMH) to inhibit histamine synthesis. alpha-FMH was given by continuous subcutaneous infusion (3 mg/kg/h) for up to 9 days. An additional oral dose of alpha-FMH (50 mg/kg) was given 2 h before each acid secretion test. Acid secretion was studied in pylorus-ligated rats and in chronic gastric fistula rats stimulated with histamine, gastrin-17, or insulin after 2-6 days of alpha-FMH infusion.

RESULTS

Treatment with alpha-FMH lowered oxyntic mucosal histamine synthesis by 80%. From previous observations this is thought to reflect depletion of histamine from the ECL cells. The remaining 20% resides in mucosal and submucosal mast cells, which seem to be resistant to alpha-FMH. Basal acid secretion was inhibited by more than 60% after alpha-FMH treatment and by more than 80% by ranitidine. Histamine-stimulated secretion was unaffected by alpha-FMH and abolished by the histamine H2-receptor antagonist ranitidine. The acid response to gastrin-17 was almost abolished in histamine-depleted rats and abolished by ranitidine. Vagally induced acid secretion (provoked by the injection of insulin or by pylorus ligation) was unaffected by alpha-FMH treatment but abolished by ranitidine and by the muscarinic M1-receptor antagonist pirenzepine.

CONCLUSION

The results suggest that gastrin stimulates acid secretion by releasing histamine from ECL cells. Vagally induced acid secretion is also dependent on a histaminergic pathway but not on ECL-cell histamine.

The protective effect of copper complexes against gastric mucosal ulcer in rats

The study examines the anti-ulcer activity of Cu(I)-(nicotinic acid)2Cl [CuCl(HNA)2]. A dose of 8 mg (23 mumol) of complex/kg body mass was suspended in 0.25% Tween-80 in saline solution and administered intragastrically to male Wistar albino rats which had developed gastric ulcers as a result of pyloric ligation (Shay-rat model). Another group of animals received 5 mg (25 mumol)/kg body mass of the copper-glycinate complex Cu(II)(glycinate)2 [Cu(II)(Gly)2]. Both protected as shown by reduction in the ulcer index, inhibition of gastric perforation and death. Significant increases in gastric juice volume and superoxide dismutase (SOD) activity in the gastric mucosa and blood plasma were found with both copper complexes, while the gastric juice prostaglandin E2 (PGE2) content was significantly decreased in the Cu(II)(Gly)2-treated group, it was significantly increased in the gastric mucosa of the CuCl(HNA)2-treated group. The copper complex-treated animals, especially those which received Cu(II)(Gly)2 had a marked fall in thromboxane A2 (TXA2) levels. These results suggest that intragastric administration of either CuCl(HNA)2 or Cu(II)(Gly)2 produced anti-ulcerogenic activity, with different modes of action.

Effects of cimetidine, atropine and pirenzepine on basal and stimulated gastric acid secretion in the rat

The gastric anti-secretagogue effects of cimetidine (a histamine H2-receptor antagonist) and of atropine (a non-selective muscarinic receptor antagonist) and pirenzepine (a selective muscarinic M1-receptor antagonist) were examined in conscious gastric fistula rats both under basal conditions and after stimulation with maximal doses of pentagastrin and histamine. Cimetidine blocked basal as well as stimulated acid secretion. The cimetidine dose-response curves and the calculated ED50 values were similar in the different experimental situations. Atropine blocked equally effectively the basal and the stimulated acid secretion. The antisecretagogue and pupil dilating effects were compared. The ED50 values for the anti-secretagogue effect and for the pupil dilating effect were in the same range though not identical. Pirenzepine blocked acid secretion, whether basal or stimulated, with similar potency. It was much more potent to block acid secretion than to cause pupil dilatation. The greater potency of pirenzepine to block acid secretion than to cause pupil dilatation suggests that the cholinergic pathway of acid secretion involves neuronal muscarinic M1-receptors within the intramural ganglia of the stomach wall. In conclusion, cimetidine, atropine and pirenzepine effectively blocked basal as well as pentagastrin- and histamine-stimulated acid secretion, indicating that both histamine and acetylcholine are important in the control of the parietal cell. Histamine has been claimed to be the final common chemical mediator of acid secretion. This view is at odds with the fact that muscarinic blocking agents also inhibit basal and stimulated acid secretion.

Endocrine cells and parietal cells in the stomach of the developing rat

Gastrin-immunoreactive cells were fairly numerous in the pancreas and upper duodenum of the rat at about the time of birth. A minor population of these cells stained with antibodies directed against the N-terminal region of gastrin-34 as well as with antibodies directed against the C-terminal region. The remainder of the cells stained with the C-terminally directed antibodies only. Within a fortnight after birth all gastrin-immunoreactive cells disappeared from the pancreas and were greatly reduced in number in the duodenum; those that remained were probably CCK cells. Gastrin cells were rare in the antrum at birth and remained rare during the first days after birth. They increased in number, slowly until after weaning (15-20 days of age) and then more rapidly, until 25-30 days of age when the gastrin cell density reached that in adult rats. At the time of birth the gastrin concentration in serum was low; the subsequent increase during the first 2 weeks paralleled the development of the antral gastrin cell system. Adult postprandial serum gastrin concentrations were reached 12 days after birth. Somatostatin cells were rare in both the antral and oxyntic mucosa at birth. They increased gradually in number until about a month after birth when the cell density reached that seen in adult rats. In the oxyntic mucosa the ECL and A-like cells are the predominant endocrine (argyrophil) cell types. They were not detected until about 4 days after birth. Their number increased slowly until about 30 days of age. They did not stain argyrophil until about 2-4 weeks after birth. Parietal cells were few at birth; ultrastructurally they appeared to be in an active state and histochemically they were shown to contain carbonic anhydrase. The pH of the gastric content of newborn rats was close to 5; 15-17 days after birth the pH was about 4 in freely fed rats. In fasted rats shortly after birth the pH was about 4. Two weeks later it was around 2, which is the pH measured in older rats. Hence, the full capacity for acid secretion is probably not established until weaning. Fasting greatly lowers the serum gastrin concentration and the histidine decarboxylase activity of the ECL cells in adult rats. Before weaning, fasting produced these effects only to a minor degree.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of gastric acid response to pylorus ligation: effects of nephrectomy

In the rat nephrectomy raises the serum gastrin concentration but makes the parietal cells refractory to gastrin. Pylorus ligation stimulates the gastric acid output by a long vago-vagal reflex in innervated animals and by an intramural reflex in chronically vagotomized animals. Nephrectomy reduced the acid response to pylorus ligation in vagally intact rats but enhanced it in vagotomized rats. The acid response to pylorus ligation in all the experimental groups was inhibited by a muscarinic blocker, atropine, and by an H2-antagonist, metiamide. The serum gastrin concentration was raised by nephrectomy and by vagal denervation. Histamine mobilization from gastric endocrine cells is reflected in the activity of gastric histidine decarboxylase. The enzyme activity in pylorus-ligated innervated rats was raised by pentagastrin, atropine, and metiamide. In nephrectomized rats the basal enzyme activity was high, and it was raised further, slightly but significantly, by pentagastrin. The basal enzyme activity in pylorus-ligated rats was also quite high after vagotomy, and it was raised further by pentagastrin. After vagotomy + nephrectomy the basal enzyme activity was very high; it was not raised further by pentagastrin. It appears that both vago-vagal and intramural reflexes involve a cholinergic and a histaminergic pathway, that gastrin is not important for the neurally mediated acid response elicited by pylorus ligation, and that the postulated histaminergic pathway does not involve histamine derived from the gastric endocrine-like cells.