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

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.

The autonomic nervous system regulates gastric ghrelin secretion in rats

Plasma ghrelin levels are responsive to short- and long-term nutrient fluctuation, but the mechanisms of its regulation are largely unknown. To explore the role of the autonomic nervous system in the regulation of ghrelin secretion, we measured plasma ghrelin levels after administration of cholinergic and adrenergic agents in rats under normally fed and 48-h fasting conditions. To assess the short- and long-term effects of vagotomy on ghrelin secretion, plasma ghrelin levels and stomach ghrelin levels and gene expressions were measured in rats subjected to fed or fasting. Additionally, we investigated whether plasma ghrelin levels were affected by the anorexigenic gastrointestinal peptides cholecystokinin and somatostatin. In the pharmacological study, plasma ghrelin levels were increased by a muscarinic agonist, an alpha-adrenergic antagonist, and a beta-adrenergic agonist, and decreased by a muscarinic antagonist and an alpha-adrenergic agonist. Vagotomy inhibited ghrelin secretion acutely, but promoted ghrelin release from the stomach at later time points. Stomach ghrelin mRNA levels were unchanged after fasting, but were significantly upregulated in vagotomized rats. The change of plasma ghrelin levels in nutrient fluctuation was independent of the endogenous effects of cholecystokinin and somatostatin. This study demonstrates that stomach ghrelin secretion is modulated by both the cholinergic and adrenergic arms of the autonomic nervous system. The dissociation between the short- and long-term effects of vagotomy on plasma ghrelin level indicates that an additional neural control mechanism might be involved in the regulation of ghrelin secretion.

Effects of cannabinoid receptor agonists on rat gastric acid secretion: discrepancy between in vitro and in vivo data

The effects of the cannabinoid (CB)-receptor agonists WIN55,212-2 and HU-210 and the selective CB(1)-receptor antagonist SR141716A were tested on in vitro and in vivo acid secretion assays from the rat. In the isolated gastric fundus from immature rats, WIN55,212-2 (0.001-30 microM), HU-210 (0.001-10 microM), or SR141716A (0.1-10 microM) did not change the basal acid output or acid responses to histamine, pentagastrin, or electrical field stimulation. HU-210 (0.3 micromol/kg, intravenously) inhibited the acid response to pentagastrin in anesthetized adult, young, or immature rats with lumen-perfused stomachs; moreover, HU-210 reduced vagally induced acid secretion in adult animals, its antisecretory effect being reversed by SR141716A (0.65 micromol/kg, intravenously). In vitro and in vivo data indicate that CB(1) receptors are not located on parietal cells but, rather, on vagal pathways (possibly at preganglionic sites) supplying the gastric mucosa. The lack of effect of CB-receptor ligands in vitro cannot be ascribed to the use of immature rats, since HU-210 inhibited stimulated acid secretion in vivo, irrespective of the animal age.

Genetic dissection of the signaling pathways that control gastric acid secretion

Gastric acid secretion is regulated by endocrine, paracrine and neurocrine signals via at least three pathways, the gastrin-histamine pathway, the CCK-somatostatin pathway and the neural pathway. Genetically-engineered mice, subjected to targeted gene disruption (i.e., knockout mice), have been used to dissect the signaling pathways that are responsible for the complexity of the regulation of acid secretion in vivo. Both gastrin knockout and gastrin/CCK2 receptor knockout mice displayed greatly impaired acid secretion, presumably because of the loss of the gastrin-histamine pathway. Gastrin/CCK double-knockout mice had a relatively high percentage of active parietal cells with a maintained ability to respond with copious acid secretion to pylorus ligation-evoked vagal stimulation and to a histamine challenge. The low acid secretion in gastrin knockout mice and gastrin/CCK2 receptor knockout mice and the restoration of acid secretion in gastrin/CCK double-knockout mice suggest that CCK plays an important role as inhibitor of the parietal cells via the CCK-somatostatin pathway by stimulating the CCK1 receptor of the D cell. In the absence of both the gastrin-histamine and the CCK-somatostatin pathway (as in gastrin/CCK2 receptor double-knockout mice), the control of acid secretion is probably taken over by neural pathways, explaining the high acid output. The observations illustrate the complexity and plasticity of the acid regulatory mechanisms. It seems that one pathway may be suppressed or allowed to dominate over the others depending on the circumstances.

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.

Altered control of gastric acid secretion in gastrin-cholecystokinin double mutant mice

BACKGROUND & AIMS

Three pathways control gastric acid secretion: the gastrin-enterochromaffin-like (ECL) cell axis, the vagus-parietal cell axis, and the cholecystokinin (CCK)-D cell axis. Mice lacking gastrin or both gastrin and CCK were examined to determine the role of the hormones.

METHODS

Acid was measured after pylorus ligation, and biopsies from gastrin knockout (KO), gastrin-CCK double-KO, and wild-type (WT) mice were collected for biochemical, immunocytochemical, and electron-microscopic examination.

RESULTS

The ECL cells were inactive in both groups of mutant mice but the cell number was unaffected. Both parietal cell number and level of H(+)/K(+)-ATPase messenger RNA (mRNA) were reduced in the mutant strains, but gastrin-CCK double-KO mice displayed more active parietal cells and larger acid output than the gastrin KO mice. The acid response to histamine in double-KO mice was unchanged whereas that to gastrin was diminished, but it could be restored by infusion of gastrin. Oxyntic D-cell density was the same in both mutant strains, but the D cells were more active in the gastrin KO than in the double-KO mice. CCK infusion in gastrin-CCK double-KO mice raised the somatostatin mRNA level and inhibited acid secretion to the level seen in gastrin KO mice. Vagotomy and atropine abolished acid secretion in all 3 groups of mice.

CONCLUSIONS

Lack of gastrin impairs the gastrin-ECL axis, whereas lack of gastrin and CCK impairs both hormonal pathways. In the gastrin-CCK double-KO mice, acid secretion is only controlled by cholinergic vagal stimulation, which normalizes the acid output.

Gastric antisecretory role and immunohistochemical localization of cannabinoid receptors in the rat stomach

1. The role of cannabinoid (CB) receptors in the regulation of gastric acid secretion was investigated in the rat by means of functional experiments and by immunohistochemistry. 2. In anaesthetized rats with lumen-perfused stomach, the non selective CB-receptor agonist WIN 55,212-2 (0.30 - 4.00 micromol kg(-1), i.v.) and the selective CB(1)-receptor agonist HU-210 (0.03 - 1.50 micromol kg(-1), i.v.), dose-dependently decreased the acid secretion induced by both pentagastrin (30 nmol kg(-1) h(-1)) and 2-deoxy-D-glucose (1.25 mmol kg(-1), i.v.). By contrast, neither WIN 55,212-2 (1 - 4 micromol kg(-1), i.v.) nor HU-210 (0.03 - 1.50 micromol kg(-1), i.v.) did modify histamine-induced acid secretion (20 micromol kg(-1) h(-1)). The selective CB(2)-receptor agonist JWH-015 (3 - 10 micromol kg(-1), i.v.) was ineffective. 3. The gastric antisecretory effects of WIN 55,212-2 and HU-210 on pentagastrin-induced acid secretion were prevented by the selective CB(1)-receptor antagonist SR141716A (0.65 micromol kg(-1), i.v.) and unaffected by the selective CB(2)-receptor antagonist SR144528 (0.65 - 2 micromol kg(-1), i.v.). 4. Bilateral cervical vagotomy and ganglionic blockade with hexamethonium (10 mg kg(-1), i.v., followed by continuous infusion of 10 mg kg(-1) h(-1)) significantly reduced, but not abolished, the maximal inhibitory effect of HU-210 (0.3 micromol kg(-1), i.v.) on pentagastrin-induced acid secretion; by contrast, pretreatment with atropine (1 mg kg(-1), i.v.) did not modify the antisecretory effect of HU-210. 5. Immunoreactivity to the CB(1) receptor was co-localized with that of the cholinergic marker choline acetyltransferase in neural elements innervating smooth muscle, mucosa and submucosal blood vessels of rat stomach fundus, corpus and antrum. In contrast, CB(2) receptor-like immunoreactivity was not observed. 6. These results indicate that gastric antisecretory effects of cannabinoids in the rat are mediated by suppression of vagal drive to the stomach through activation of CB(1) receptors, located on pre- and postganglionic cholinergic pathways. However, the ineffectiveness of atropine in reducing the effect of HU-210 suggests that the release of non cholinergic excitatory neurotransmitters may be regulated by CB(1) receptors.

Neurohormonal regulation of secretion from isolated rat stomach ECL cells: a critical reappraisal

ECL cells are endocrine/paracrine cells in the oxyntic mucosa. They produce, store and secrete histamine and chromogranin A-derived peptides such as pancreastatin. The regulation of ECL-cell secretion has been studied by several groups using purified ECL cells, isolated from rat stomachs. Reports from different laboratories often disagree. The purpose of the present study was to re-evaluate the discrepancies by studying histamine (or pancreastatin) secretion from standardized preparations of pure, well-functioning ECL cells. Cells from rat oxyntic mucosa were dispersed by pronase digestion, purified by repeated counter-flow elutriation and subjected to density gradient centrifugation. The final preparation consisted of more than 90% ECL cells (verified by histamine and/or histidine decarboxylase immunocytochemistry). They were maintained in primary culture for 48 h before they were exposed to candidate stimulants and inhibitors for 30 min after which the medium was collected for determination of mobilized histamine (or pancreastatin). Gastrin-17 and sulphated cholecystokinin octapeptide (CCK-8s) raised histamine secretion 4-fold, the EC(50) for both peptides being around 100 pM. The neuropeptide pituitary adenylate cyclase activating peptide (PACAP-27) (5-fold increase) and the related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) (3-fold increase) mobilized histamine with similar potency (EC(50) ranging from 80 to 140 pM). Adrenaline, isoprenaline and terbutaline stimulated secretion by activating a beta2 receptor subtype, while acetylcholine and carbachol were without effect. Secretion experiments were invariably run in parallel with a gastrin standard curve. Somatostatin, prostaglandin E2 (PGE2) and the PGE1 congener misoprostol inhibited PACAP- and gastrin-stimulated secretion by more than 90%, with IC(50) values ranging from 90-720 (somatostatin) to 40-200 (misoprostol) pM. The neuropeptide galanin inhibited secretion by 60-70% with a potency similar to that of somatostatin. Proposed inhibitors such as peptide YY, neuropeptide Y and the cytokines interleukin 1-beta and tumor necrosis factor alpha induced at best a moderate inhibition of gastrin- or PACAP-stimulated secretion at high concentrations, while calcitonin gene-related peptide, pancreatic polypeptide and histamine itself were without effect. Inhibition of gastrin- or PACAP-stimulated secretion was routinely compared to a somatostatin standard curve. In conclusion, gastrin, PACAP, VIP/PHI and adrenaline stimulated secretion. Somatostatin and PGE2 were powerful inhibitors of both gastrin- and PACAP-stimulated secretion; although equally potent, galanin was less effective than somatostatin and PGE2.

Sustained cholecystokinin-B/gastrin receptor blockade does not impair basal or histamine-stimulated acid secretion in chronic gastric fistula rats

Gastrin is a physiologically important secretagogue. It is thought to stimulate parietal cells indirectly by mobilizing histamine from enterochromaffin-like (ECL) cells in the oxyntic mucosa. Gastrin stimulates the secretory activity and growth of the ECL cells via an action on cholecystokinin-B/gastrin receptors. Acute cholecystokinin-B/gastrin receptor blockade is known to inhibit gastrin-stimulated acid secretion but whether sustained cholecystokinin-B/gastrin receptor blockade will impair basal, gastrin- and histamine-stimulated acid secretion remains uncertain. The present study was designed to study the effect of long-term (4 weeks) cholecystokinin-B/gastrin receptor blockade on basal and stimulated acid secretion in conscious rats. The selective cholecystokinin-B/gastrin receptor antagonist YM022 (3 mumol.kg-1.hr-1) was given to gastric fistula rats by continuous subcutaneous infusion via osmotic minipumps for various times from 2 hr to 4 weeks. Basal, gastrin- and histamine-stimulated acid secretion were examined during and after cessation of treatment. Basal and histamine-stimulated acid secretion was not affected by YM022 during the 4 week period of administration, whereas gastrin-induced acid secretion was inhibited. YM022 induced hypergastrinaemia in freely fed rats but did not affect the serum gastrin level in fasted rats. The serum gastrin concentration and gastrin-induced acid secretion returned to control levels 3-7 days after termination of YM022 administration.

The trophic response of rat pancreas to sulfated cholecystokinin-8 is dose- and time-dependent and not affected by vagotomy or atropine

Cholecystokinin (CCK) stimulates pancreatic enzyme secretion and growth. This study establishes the dose/plasma concentration--and time--response relationships for the trophic effect of CCK on the rat pancreas and evaluates the importance of vagal innervation and muscarinic receptors for the trophic effect. Rats received sulfated CCK-8 (CCK-8s) by continuous subcutaneous infusion. Different doses and different times of treatment were tested. The trophic effect was determined as wet weight and DNA content of the pancreas. The pancreatic weight and DNA content were found to depend not only on the plasma concentration of CCK-8s but also on the duration of treatment. The EC50 value was 40 pmoles CCK-8s per liter. This value should be compared with plasma CCK-8s concentrations of 2-4 pmol/l in intact fed rats. Maximum trophic effect was observed after 7-14 days of infusion. We conclude that although physiologically relevant concentrations of CCK-8s may be important for the maintenance of the pancreas they do not induce growth. In another experiment atropinized, vagally denervated and intact rats were treated with a maximally effective dose of CCK for four days. The trophic effect of CCK-8s was unaffected by vagotomy or atropinization.

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.

Comparative evaluation of the role of endogenous gastrin in basal acid secretion in conscious rats provided with chronic fistula and pylorus ligation

We determined the relative contributions of endogenous gastrin, histamine and cholinergic tone to basal acid secretion in chronic fistula rats. Results were compared with those for acid secretion in pylorus-ligated rats. In chronic fistula rats, YM022 ¿(R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1 H-1,4-benzodiazepin-3-yl]-3-(3-methylphenyl)urea¿ dose-dependently inhibited pentagastrin-stimulated acid secretion and abolished this secretion at 1 mumol/kg, s.c., but did not affect histamine- and carbachol-induced acid secretion even at 10 mumol/kg. In contrast, famotidine at 1 mumol/kg completely inhibited not only the acid secretion induced by histamine but also those by pentagastrin and carbachol. Furthermore, atropine abolished carbachol- and pentagastrin-stimulated acid secretion and significantly suppressed histamine-stimulated acid secretion at 0.1 mumol/kg. YM022 dose-dependently inhibited basal acid secretion. The YM022 dosage required to inhibit basal acid secretion is consistent with that required to suppress pentagastrin-induced acid secretion. Famotidine (1 mumol/kg) and atropine (0.1 mumol/kg) also abolished basal acid secretion. In pylorus-ligated rats, YM022 inhibited acid secretion in a dose-dependent manner; the inhibition at 1 mumol/kg, i.v. was 65%. No additional effect was observed when rats were dosed at 30 mumol/kg. Famotidine partially inhibited acid secretion in these rats, whereas atropine abolished this secretion. These results indicate that the major part of basal acid secretion in rats is attributable to endogenous gastrin via histamine- and cholinergic tone-dependent pathways. Moreover, pylorus ligation reduces the relative contribution of gastrin to acid secretion due to the activation of cholinergic tone.

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 role of peripheral opioid receptor subtypes in the modulation of gastric acid secretion and plasma gastrin in dogs

The peripheral opioid receptor subtypes involved in the regulation of gastric acid secretion were studied in dogs with both a gastric fistula and a Heidenhain pouch, by using the putative mu-opioid receptor agonist dermorphin, the delta-opioid receptor agonist [D-Ala2,D-Leu5]enkephalin (DADLE) and the kappa-opioid receptor agonist dynorphin-(1-13). Dermorphin caused a significant increase in basal acid secretion from both the gastric fistula and the Heidenhain pouch, while DADLE and dynorphin-(1-13) did not. Acid secretion stimulated by 2-deoxy-D-glucose from the gastric fistula was not modified by dermorphin and dynorphin-(1-13), while DADLE significantly inhibited it; at the same time gastric secretion from the Heidenhain pouch was significantly increased by dermorphin and unmodified by DADLE and dynorphin-(1-13). Dermorphin, DADLE or dynorphin-(1-13) did not modify plasma gastrin during basal or 2-deoxy-D-glucose-stimulated conditions. Submaximal bethanechol-stimulated secretion was increased by dermorphin and DADLE but unaffected by dynorphin-(1-13). Acid secretion from the gastric fistula stimulated by pentagastrin was enhanced by dermorphin, inhibited by DADLE and unaffected by dynorphin-(1-13). Dermorphin and DADLE significantly increased acid secretion from the Heidenhain pouch stimulated by pentagastrin, while dynorphin-(1-13) was ineffective. Naloxone prevented the stimulatory effects of dermorphin and DADLE on the Heidenhain pouch, but it reduced acid secretion from the gastric fistula further when given with DADLE. The inhibitory effects of DADLE on secretion from the gastric fistula were prevented by naltrindole, a selective antagonist of delta-opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Histamine-producing cells in the stomach and their role in the regulation of acid secretion

Histamine H2-receptor antagonists inhibit basal and all kinds of stimulated acid secretion with about the same effectiveness, and hence, local release of histamine is thought to be necessary for the stimulation of parietal cells. A local histamine pool is physiologically relevant only if it is within the diffusion distance of the parietal cells, if it is effectively mobilized by gastrin, and if it is endowed with the machinery for a rapid replenishment of the histamine that has been released. Histamine in the stomach occurs in endocrine cells (so-called enterochromaffin-like (ECL) cells), mast cells, and neurons. The ECL cells are peptide hormone-producing cells. In mammals they are located basally in the oxyntic gland area, in the chief-cell-rich region. Parietal cells predominate in t he mid-region. ECL cells respond readily to gastrin with histamine release and histamine resynthesis. Thus, the ECL cells fulfil important prerequisites of a physiologically relevant histamine pool. however, it is not apparent how the preferential localization of ECL cells at the base of the glands may be conducive to a direct effect of released histamine ont he parietal cells, unless histamine reaches the parietal cells via capillary transport from the glandular base. Mast cells are numerous int he stomach of, for example, man, pigs, dogs, and cats. They occur scattered throughout the stomach wall without any obvious relation to the parietal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of some antisecretory drugs on acid production, intracellular free Ca2+, and cyclic AMP production in isolated pig parietal cells

The effects of some inhibitors of acid secretion were tested on isolated, purified pig parietal cells. The cells were stimulated with 10(-4) M histamine, 10(-5) M carbachol, or 10(-7) M pentagastrin. The H,K-ATPase inhibitors SCH 28080 and omeprazole inhibited both the basal and secretagogue-stimulated acid production, as measured by aminopyrine accumulation, irrespective of the type of stimulator used. The IC50 value was 3-5 x 10(-9) M for SCH 28080 and 1-3 x 10(-8) M for omeprazole. Ranitidine inhibited the histamine-stimulated but not the basal acid production. The IC50 value was 2 x 10(-5) M. Stimulation of acid production with carbachol was blocked by pirenzepine, with an IC50 of 6 x 10(-7) M. Pirenzepine (10(-5) M) specifically blocked the carbachol-stimulated increase in cytosolic free Ca2+ in fura-2-loaded cells but not the increase in cytosolic free Ca2+ induced by histamine or pentagastrin. Ranitidine (10(-4) M) prevented the histamine-induced increase in Ca2+ and was also the only one of the four inhibitors which prevented the histamine-stimulated cAMP formation. SCH 28080 (10(-5) M) significantly potentiated the histamine-stimulated increase in cytosolic free Ca2+ and the formation of cAMP, whereas omeprazole (10(-5) M) was without effect.