gastrins and alpha-fluoromethylhistidine

Rat stomach ECL cells release histamine in response to gastrin. Submucosal microinfusion of endothelin or adrenaline, known to cause vasoconstriction and gastric lesions, mobilized striking amounts of histamine. While the histamine response to gastrin is sustainable for hours, that to endothelin and adrenaline was characteristically short-lasting (1-2 h). The aims of this study were to identify the cellular source of histamine mobilized by endothelin and adrenaline, and examine the differences between the histamine-mobilizing effects of gastrin, and of endothelin and adrenaline. Endothelin, adrenaline or gastrin were administered by submucosal microinfusion. Gastric histamine mobilization was monitored by microdialysis. Local pretreatment with the H1-receptor antagonist mepyramine and the H2-receptor antagonist ranitidine did not prevent endothelin- or adrenaline-induced mucosal damage. Submucosal microinfusion of histamine did not cause damage. Acid blockade by ranitidine or omeprazole prevented the damage, suggesting that acid back diffusion contributes. Gastrin raised histidine decarboxylase (HDC) activity close to the probe, without affecting the histamine concentration. Endothelin and adrenaline lowered histamine by 50-70%, without activating HDC. Histamine mobilization declined upon repeated administration. Endothelin reduced the number of histamine-immunoreactive ECL cells locally, and reduced the number of secretory vesicles. Thus, unlike gastrin, endothelin (and adrenaline) is capable of exhausting ECL-cell histamine. Microinfusion of alpha-fluoromethylhistidine (known to deplete ECL cells but not mast cells of histamine) reduced the histamine-mobilizing effect of endothelin by 80%, while 1-week pretreatment with omeprazole enhanced it, supporting the involvement of ECL cells. Somatostatin or the prostanoid misoprostol inhibited gastrin-, but not endothelin-stimulated histamine release, suggesting that endothelin and gastrin mobilize histamine via different mechanisms. While gastrin effectively mobilized histamine from ECL cells in primary culture, endothelin had no effect, and adrenaline, a modest effect. Hence, the striking effects of endothelin and adrenaline on ECL cells in situ are probably indirect, possibly a consequence of ischemia.

Topics: Animals; Cells, Cultured; Endothelins; Enterochromaffin-like Cells; Epinephrine; Female; Gastric Mucosa; Gastrins; Histamine; Histamine Release; Histidine Decarboxylase; Infusions, Parenteral; Male; Methylhistidines; Microdialysis; Microinjections; Misoprostol; Omeprazole; Parietal Cells, Gastric; Pyrilamine; Ranitidine; Rats; Rats, Sprague-Dawley; Somatostatin; Time Factors

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

Topics: Animals; Benzodiazepines; Chromogranin A; Enterochromaffin-like Cells; Enzyme Inhibitors; Fluorescent Antibody Technique; Food; Gastric Mucosa; Gastrins; Histamine; Hormone Antagonists; Male; Methylhistidines; Microdialysis; Pancreatic Hormones; Rats; Rats, Sprague-Dawley; Time Factors; Vagotomy, Proximal Gastric

The present study investigated (1) the pharmacological profile of cholecystokinin (CCK) receptor subtypes involved in the regulation of gastric pepsinogen secretion, (2) the influence of gastric acidity on peptic responses induced by CCK-8-sulfate (CCK-8S) or gastrin-I; and (3) the mechanisms accounting for the effects of CCK-like peptides on pepsinogen secretion. In anaesthetized rats, i.v. injection of CCK-8S or gastrin-I increased both pepsinogen and acid secretion. The pepsigogue effect of CCK-8S was higher than that of gastrin-I, whereas acid hypersecretion after CCK-8S was lower than that induced by gastrin-I. Peptic output following CCK-8S was partly blocked by i.v. injection of the CCK1 receptor antagonist, devazepide (-75.3%), or the CCK2 receptor antagonist, L-365,260 [3R(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3 yl)-N'-(3-methyl-phenyl)urea; -27.9%], but was fully prevented by combined administration of devazepide and L-365,260. The gastric acid hypersecretory effect of CCK-8S was enhanced by devazepide (+84.5%) and blocked by L-365,260. In contrast, the gastric secretory actions of gastrin-I were insensitive to devazepide, but abolished by L-365,260. Excitatory effects of CCK-8S and gastrin-I were not modified by vagotomy or atropine, whereas cimetidine or alpha-fluoromethylhistidine (irreversible blocker of histidine decarboxylase) partly prevented acid hypersecretion induced by both peptides without affecting their pepsigogue effects. After pretreatment with omeprazole, both CCK-8S and gastrin-I failed to stimulate acid secretion, while they increased pepsinogen output. In rats with gastric perfusion of acid solutions, CCK-8S or gastrin-I increased peptic output in a pH-independent manner either with or without pretreatment with omeprazole. Ablation of capsaicin-sensitive sensory nerves as well as application of lidocaine to the gastric mucosa failed to modify the excitatory effects of CCK-8S or gastrin-I on pepsinogen and acid secretion. Blockade of the nitric oxide (NO) synthase pathway by N(G)-nitro-L-arginine-methyl ester prevented the pepsigogue actions of both CCK-8S and gastrin-I (-61.8% and -71.7%, respectively), without affecting the concomitant increase in acid output. In addition, both these peptides significantly increased the release of NO breakdown products into the gastric lumen. The present results suggest that: (1) both CCK1 and CCK2 receptors mediate the peptic secretory responses induced by CCK-like

Topics: Acids; Anesthetics, Local; Animals; Benzodiazepinones; Capsaicin; Devazepide; Dose-Response Relationship, Drug; Enzyme Inhibitors; Gastric Acid; Gastric Mucosa; Gastrins; Histidine Decarboxylase; Hormone Antagonists; Lidocaine; Male; Methylhistidines; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide; Nitrites; Nootropic Agents; Omeprazole; Pepsinogens; Perfusion; Phenylurea Compounds; Rats; Rats, Wistar; Receptors, Cholecystokinin; Sincalide; Somatostatin; Vagotomy

Ageing cells, especially post-mitotic cells, are known to accumulate pigments, i.e. highly electron-dense material, referred to as ceroid or lipofuscin. This material is formed as a consequence of autophagocytosis and peroxidation of the products undergoing degradation. The present study describes the development of lipofuscin in the ECL cells of the rat stomach. These cells produce and secrete histamine in response to gastrin. They are rich in secretory vesicles, which fuse to form vacuoles in hypergastrinaemic rats. Hypergastrinaemia was induced by continuous infusion of human Leu15-gastrin-17 for 6 days or by daily treatment with omeprazole for 10 weeks. Either treatment caused both vacuoles and lipofuscin bodies to appear in large numbers; the vacuoles disappeared promptly after interruption of the hypergastrinaemia, whereas the lipofuscin bodies remained. Antrectomy-evoked hypogastrinaemia was associated with a reduced number and volume density of lipofuscin bodies. Treatment with alpha-fluoromethylhistidine, an irreversible inhibitor of the histamine-forming enzyme, resulted in depletion of ECL-cell histamine and was found to prevent the omeprazole-evoked formation of vacuoles and lipofuscin. The numbers of both vacuoles and lipofuscin bodies were well-correlated with the serum gastrin concentration, suggesting that gastrin stimulates the development not only of vacuoles but also of lipofuscin, perhaps through enhanced autophagocytosis and/or oxidative stress. Thus, lipofuscin bodies may develop from vacuoles, and both vacuoles and lipofuscin bodies may reflect the efforts of overstimulated ECL cells to cope with the excessive formation of secretory products.

Topics: Animals; Cellular Senescence; Enzyme Inhibitors; Gastrectomy; Gastric Mucosa; Gastrins; Histamine Release; Histidine Decarboxylase; Humans; Lipofuscin; Male; Methylhistidines; Omeprazole; Oxidative Stress; Phagocytosis; Pyloric Antrum; Rats; Rats, Sprague-Dawley; Stomach; Time Factors; Vacuoles

In this study we investigated the short-term effect of somatostatin on histamine synthesis in a cell population isolated from rabbit gastric mucosa and enriched in enterochromaffin-like cells. Somatostatin inhibited basal and gastrin-stimulated histamine synthesis through a dual mechanism involving a decrease in the affinity of histidine decarboxylase (HDC) for its substrate (L-histidine) and a reduction in the number of functional HDC molecules. H-89 (an inhibitor of cAMP-dependent protein kinase) mimicked somatostatin-induced reduction of HDC affinity, which, on the contrary, was selectively reversed by pertussis toxin (PTX). Furthermore, forskolin was shown to reverse the inhibitory effect of H-89 and to prevent the somatostatin-induced reduction in HDC affinity for L-histidine. Thus, the somatostatin-induced reduction in affinity seems to involve a PTX-sensitive G protein and an inhibition of the cAMP-dependent pathway. On the other hand, the somatostatin-induced decrease in the number of functional HDC molecules seems to be PTX insensitive and independent from a modulation of the cAMP pathway, and does not seem to involve a significant change in HDC messenger RNA expression or a regulation of protein kinase C. The exact nature of this second mechanism will need further studies to be elucidated.

Topics: Animals; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Fluorescent Antibody Technique; Gastric Mucosa; Gastrins; GTP-Binding Proteins; Histamine Antagonists; Histidine Decarboxylase; Kinetics; Male; Methylhistidines; Pertussis Toxin; Protein Kinase C; Rabbits; RNA, Messenger; Somatostatin; Stomach; Time Factors; Virulence Factors, Bordetella

Histamine-producing enterochromaffin-like (ECL) cells are numerous in the oxyntic mucosa of the rat stomach. They respond to gastrin by secretory activation, hypertrophy and hyperplasia. They contain cytoplasmic granules (median profile diameter 120 nm), secretory vesicles (180 nm) and microvesicles (70 nm). alpha-Fluoromethylhistidine (alpha-FMH) depletes histamine from the ECL cells by inhibiting the histamine-forming enzyme histidine decarboxylase. Long-term hypergastrinemia, evoked by omeprazole, increases the ECL-cell histamine concentration. The way in which chronic histamine depletion affects omeprazole-induced ECL-cell hypertrophy, and the ways in which granules and vesicles in the ECL cells respond to alpha-FMH and/or omeprazole have been studied. Rats were treated with alpha-FMH (3 mg/kg per h subcutaneously), omeprazole (400 micromol/kg per day orally), alpha-FMH+omeprazole, or vehicle for 6 weeks. ECL cell profiles in electron micrographs were analysed panimetrically. The results show that the omeprazole-evoked hypertrophy of the ECL cells is not affected by depletion of ECL-cell histamine, thereby supporting the view that ECL-cell histamine is not important for full expression of the gastrin-evoked trophic effects on the ECL cells. The loss of ECL-cell histamine following treatment with alpha-FMH and with alpha-FMH+omeprazole is associated with a greatly reduced size of the secretory vesicle compartment. The granules, on the other hand, are unaffected by alpha-FMH and alpha-FMH+omeprazole. Omeprazole treatment leads to the appearance of numerous vacuoles (with profile diameter greater than 500 nm); such vacuoles are not observed in the ECL cells of rats treated with alpha-FMH or alpha-FMH+omeprazole. The omeprazole-induced increase in ECL-cell histamine is associated with an increase in the compartment composed of secretory vesicles and vacuoles. The findings support the hypothesis that secretory vesicles (and vacuoles) represent a major storage site of ECL-cell histamine.

Topics: Animals; Cell Size; Cytoplasmic Granules; Enterochromaffin Cells; Female; Gastric Mucosa; Gastrins; Histamine Release; Methylhistidines; Omeprazole; Rats; Rats, Sprague-Dawley; Vacuoles

The ECL cells in the rat stomach release pancreastatin and histamine in response to gastrin stimulation. The present study compares the release of pancreastatin and histamine from the ECL cells and the secretion of acid from the parietal cells in response to gastrin, and examines how a markedly reduced histamine content in the ECL cells will affect the gastrin-evoked release of pancreastatin and the secretion of gastrin acid. Totally isolated, vascularly perfused stomachs were prepared from fasted rats. Some of the rats had been pre-treated for 24 h with (alpha-fluoromethylhistidine (alpha-FMH), resulting in 80% depletion of oxyntic mucosal histamine (mainly ECL-cell histamine). The stomachs were perfused with rat gastrin-17, alpha-FMH, isobutyl methylxanthine (IBMX), or vehicle in various combinations for 8 h. The venous outflow was collected (30-min samples) for determination of histamine and pancreastatin-like immunoreactivity (LI) and the gastric luminal outflow was collected for determination of H+. Gastrin raised the outflow of pancreastatin-LI and histamine but did not raise the acid output unless IBMX was added. The outflow of pancreastatin-LI and histamine was greater after gastrin + IBMX (at least during the first 4-h period) than after gastrin alone. alpha-FMH reduced gastrin-evoked histamine outflow but did not affect gastrin-evoked pancreastatin-LI outflow. Also the acid output in response to gastrin + IBMX was much reduced by alpha-FMH. In conclusion, increased levels of intracellular cAMP enhanced the gastrin-evoked release of pancreastatin-LI and histamine from the ECL cells and made it possible for histamine, released from the ECL cells, to cause acid secretion from the parietal cells. ECL-cell histamine depletion reduced the gastrin-evoked acid secretion; it did not affect the gastrin-evoked release of pancreastatin-LI.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Chromogranin A; Gastric Acid; Gastrins; Histamine Release; Histidine Decarboxylase; Male; Methylhistidines; Pancreatic Hormones; Parietal Cells, Gastric; Phosphodiesterase Inhibitors; Rats; Rats, Sprague-Dawley

Gastrin activates histidine decarboxylase (HDC) and increases HDC and chromogranin A (CGA) mRNA levels in histamine-producing enterochromaffin-like (ECL) cells in the rat stomach. We have studied how histamine depletion by subcutaneous infusion of the HDC inhibitor alpha-fluoromethyl-histidine (alpha-FMH) affects how ECL cells respond to hypergastrinemia in terms of HDC and CGA mRNA levels.. In one experiment rats received alpha-FMH for 24 h. In another experiment rats received alpha-FMH, omeprazole (perorally), or a combination of the two drugs for 10 days. In a third experiment antrectomized rats were treated with alpha-FMH for 48 h. The circulating gastrin level, oxyntic mucosal histamine concentration, HDC activity, and HDC and CGA mRNA levels were determined.. alpha-FMH for 24 h increased the HDC and CGA mRNA levels without increasing the serum gastrin concentration. alpha-FMH for 10 days increased the serum gastrin concentration twofold. alpha-FMH + omeprazole resulted in the same serum gastrin concentration as after omeprazole alone (eightfold increase). HDC mRNA levels were higher after alpha-FMH + omeprazole than after omeprazole alone. alpha-FMH alone induced an HDC mRNA level that was similar in magnitude to that observed after omeprazole, although the serum gastrin concentration after alpha-FMH was much lower. In antrectomized rats alpha-FMH increased the HDC and CGA mRNA levels without increasing the serum gastrin concentration.. ECL-cell histamine depletion will increase mRNA levels for HDC and CGA by a gastrin-independent mechanism, possibly involving abolished histamine autofeedback inhibition.

Topics: Animals; Anti-Ulcer Agents; Culture Techniques; Disease Models, Animal; Enterochromaffin Cells; Enzyme Inhibitors; Female; Gastric Mucosa; Gastrins; Histamine; Histidine Decarboxylase; Methylhistidines; Omeprazole; Rats; Rats, Sprague-Dawley; RNA, Messenger

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.. 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.. 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.. 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.

Topics: Animals; Disease Models, Animal; Enterochromaffin Cells; Enzyme Inhibitors; Female; Gastric Acid; Gastric Fistula; Gastrins; Histamine; Methylhistidines; Parietal Cells, Gastric; Rats; Rats, Sprague-Dawley

In the rat, gastric histamine is stored predominantly in the enterochromaffin-like (ECL) cells, which are located basally in the oxyntic mucosa. The functional significance of histamine in the ECL cells is a matter of speculation. In this study the effect of depletion of histamine on the properties and ultrastructure of the ECL cells was examined. Histamine synthesis was inhibited with alpha-fluoromethylhistidine (3 mg.kg-1.h-1) given via osmotic minipumps over a period of 24 h. The treatment reduced the histidine decarboxylase activity (approximately 20% remaining) and histamine concentration (less than 20% remaining) in the oxyntic mucosa, as well as the intensity of histamine- and chromogranin A-immunostaining in the ECL cells, compared to control rats. The cytoplasmic (secretory) granules/vesicles were greatly reduced in number and size following alpha-fluoromethylhistidine administration. The histamine immunostaining of the mast cells, which occurs at the mucosal surface and in the submucosa, appeared unaffected. We conclude that ECL cell histamine accounts for at least 80% of the total oxyntic mucosal histamine in the rat and that it represents a more mobile pool than mast cell histamine. The reduction in the number and size of the ECL cell granules/vesicles following histamine depletion is in accord with the idea that they represent the storage site for histamine.

Topics: Animals; Cytoplasmic Granules; Enterochromaffin Cells; Female; Gastric Mucosa; Gastrins; Histamine; Histamine Release; Histidine Decarboxylase; Methylhistidines; Rats; Rats, Sprague-Dawley

In the rat, gastric histamine is stored mainly in the enterochromaffinlike cells. Gastrin releases histamine from these cells, and long-term hypergastrinemia results in hyperplasia. The effect of sustained hypergastrinemia on histamine-depleted enterochromaffinlike cells was studied by measuring histidine decarboxylase activity and histamine concentrations and by using quantitative histology. Hypergastrinemia maintained for 6 weeks was induced by inhibition of gastric acid secretion with omeprazole (400 mumol.kg-1.day-1) given orally, and histamine synthesis was inhibited for the same length of time with alpha-fluoromethylhistidine (3 mg.kg-1.h-1) given via osmotic minipumps. In rats given omeprazole alone, the effects of the resulting hypergastrinemia on the enterochromaffinlike cells was reflected in increased histidine decarboxylase activity, increased histamine concentration, and increased number of enterochromaffinlike cells. The general trophic effects on the stomach were seen as increased stomach and oxyntic mucosal weight and increased mucosal thickness. Treatment with alpha-fluoromethylhistidine plus omeprazole markedly reduced the histidine decarboxylase activity and histamine concentration, but the weight of the stomach and oxyntic mucosa, the enterochromaffinlike cell density, and intensity of histidine decarboxylase immunostaining were increased to at least the same extent as after omeprazole alone. These observations indicate that enterochromaffinlike cell histamine is not important for a full expression of gastrin-evoked trophic effects in the stomach.

Topics: Animals; Enterochromaffin Cells; Female; Gastric Mucosa; Gastrins; Histamine; Histidine Decarboxylase; Hyperplasia; Methylhistidines; Omeprazole; Organ Size; Rats; Rats, Inbred Strains