Long-term Hypergastrinaemia Research Articles

УЛЬТРАСТРУКТУРНЕ ДОСЛІДЖЕННЯ КЛІТИН СЛИЗОВОЇ ОБОЛОНКИ ТОВСТОГО КИШЕЧНИКА ЩУРІВ ЗА ТРИВАЛОЇ ГІПЕРГАСТРИНЕМІЇ

Gastrin is considered one of the most important hormones regulating physiological processes. Trophic and proliferative effects of high gastrin levels on gastric mucosa are well known. Butinformation about gastrin effects on the colon is rather fragmentary and contradictory. In this study, ultrastructural changes in the proximal part of the colon induced in rats by chronic hypergastrinemia were analyzed by transmission electron microscopy. Experimental omeprazole-induced hypergastrinemia was reproduced using daily injections of proton pump inhibitor omeprazole in rats, resulted in hypersecrestion of gastrin by G-cells of stomach. Growth of gastrin level in the blood plasma was checked using radioimmunoassay method. Prolonged hypergastrinemia has been shown to be associated with increased cell proliferation and appearance of cellular atypia in the large intestine mucosa. The number of undifferentiated cells increased prominently. Intercellular contacts between such cells are altered, the space between them is unevenly expanded. Their organelles were observed significantly reduced, mitochondria contained destroyed crysts and signs of edema. Endocrinocytes did not contain their typical secretory granules. Cell nuclei were small, electron-dense, with invagination. In addition, numerous microorganisms were revealed in the intestinal lumen, as well as their invasion into the mucosa. Those ultrastructural changes were indicate increased hyperplastic processes and impaired cell differentiation in the epitheliocytes of large intestine. Therefore, long-term experimental hypergastrinaemia causes dysplastic changes in the large intestine mucosa of rats.

The regulation of gastric acid secretion – clinical perspectives

The purpose of this review, based upon 40years of research, is to clear old controversies. The gastric juice is a strong acid with active enzymes (pepsin and lipase); ideal for killing swallowed microorganisms. Totally isolated rat stomach and histamine determination. Human gastric carcinomas were examined for ECL cell differentiation because tumours found in rodents after dosing with inhibitors of acid secretion were reclassified to be of ECL cell origin. The gastrin receptor is localized to the ECL cell only, where gastrin stimulates the function and growth. Drug-induced hypo-acidity induces hypergastrinaemia and ECL cell hyperplasia responsible for rebound acid hypersecretion. Every condition with long-term hypergastrinaemia disposes to ECL cell neoplasia. In man, both atrophic gastritis and gastrinoma lead to ECL cell carcinoids. Proton pump inhibitors induce hypergastrinaemia with ECL cell hyperplasia and ECL cell carcinoids that disappear when stopping treatment. The gastrin antagonist netazepide induces regression of ECL cell carcinoids due to atrophic gastritis. Human gastric carcinomas of diffuse type, particularly the signet-ring subtype, show ECL cell differentiation, suggesting involvement of gastrin in the carcinogenesis. Helicobacter pylori (Hp) causes gastritis and peptic ulcer, and when infecting the antrum only gives a slight hypergastrinaemia with acid hypersecretion predisposing to duodenal ulcer, but protecting from gastric cancer. When Hp infection spreads to oxyntic mucosa, it induces atrophy, reduced acid secretion and marked hypergastrinaemia and cancer.It is remarkable that the interaction between Hp and gastrin may explain the pathogenesis of most diseases in the upper gastrointestinal tract.

Changes in gene expression of gastric mucosa during therapeutic acid inhibition

Long-term therapy with potent acid inhibitors is a common treatment for gastro-esophageal reflux disease. Administration of proton pump inhibitors (PPIs) causes profound and continuous hypochlorhydria by inhibition of the proton pump in gastric parietal cells. Long-term hypergastrinaemia increases mucosal thickness and enterochromaffin-like cell density in oxyntic mucosa. The aim of this study was to see whether this very common clinical intervention induces significant changes in the gastric mucosal gene expression pattern. Seven patients suffering from gastro-esophageal reflux disease were included in this study. Endoscopic biopsies were taken from the corpus mucosa before and toward the end of a 3-month treatment with the PPI esomeprazole. Microarray analysis identified 186 differentially expressed genes. A high proportion of genes with changed gene expression levels during PPI treatment are involved in proliferation, apoptosis, and stress response. This study identified many genes that were not previously known to be affected by inhibition of gastric acid secretion. Further characterization of the functional roles of genes whose expression is modulated by potent acid inhibition may give new insight into the biological responses to potent acid inhibition, including the mucosal response to the moderately increased gastrin levels encountered in clinical practice.

Mobilization of rat stomach ECL-cell histamine in response to short- or long-term treatment with omeprazole and/or YF 476 studied by gastric submucosal microdialysis in conscious rats.

1. Mobilization of histamine from the ECL cells was monitored by gastric submucosal microdialysis in conscious rats. The ECL cells are known to operate under gastrin control and the purpose of the present study was to examine their in situ response to short-term (12 h) as well as long-term (28 days) hypergastrinaemia, induced by treatment with the proton pump inhibitor omeprazole. 2. Hypergastrinaemia promptly raised the histamine concentration in the microdialysate. The effect was prevented by CCK(2) receptor blockade (YF476). On day 7 of omeprazole treatment the microdialysate histamine concentration reached a peak, five times higher than before treatment. Subsequently (14 and 28 days), less histamine was mobilized. 3. Gastrin infusion (4 h) raised the microdialysate histamine concentration in a dose-dependent manner in fasted rats and freely fed rats and in rats treated with omeprazole for a week. However, while fasted and fed rats responded to low doses of gastrin, the omeprazole-treated rats required large doses of gastrin to respond. 4. When the amount of histamine mobilized was related to the serum gastrin concentration the following EC(50) values could be calculated: fasted rats 2.3 x 10(-10) M, freely fed rats 2.5 x 10(-10) M, omeprazole-treated rats 8.7 x 10(-10) M. The maximal histamine responses in the three groups were 18.4 pmol 4 h(-1)+/-0.8, 21.9 pmol 4 h(-1)+/-1.2 and 68.0 pmol 4 h(-1)+/-3.5, respectively. 5. The results suggest that ECL cells, exposed to a high gastrin concentration for a week, respond with a shift in the receptor-ligand binding affinity from high to low. Apparently, CCK(2) receptors of the ECL cells are subject to dynamic changes with respect to ligand-binding affinity.

Gastrin effects on isolated rat enterochromaffin-like cells following long-term hypergastrinaemia in vivo

The enterochromaffin-like (ECL) cells play an important role in the regulation of gastric acid secretion. They respond to gastrin by a prompt increase in histamine secretion, an effect which is mediated by the CCK- B/gastrin receptor acting through the IP 3/DAG pathway. In the rat, long-term treatment with acid secretion inhibitors induces hypergastrinaemia which, in turn, results in ECL cell hypertrophy and hyperplasia. The aim of the present study was to evaluate various functional parameters in acutely isolated rat ECL cells, following long-term hypergastrinaemia in vivo. Rats were treated with vehicle or a supramaximal daily dose of omeprazole for more than 10 weeks to ensure ECL cell hyperplasia. ECL cells were isolated from vehicle-treated animals and 24, 72 and 120 h after the last dose of omeprazole. The functional activity of the acutely isolated ECL cells was determined by measuring gastrin-and forskolin-induced histamine secretion. Changes in cytosolic free calcium upon gastrin stimulation were monitored by digital video imaging. ECL cells successively regained their ability to respond to gastrin following long-term hypergastrinaemia, reaching close to vehicle-treated levels 120 h after the last dose of omeprazole. In the rat, the response pattern of the ECL cells appears to normalise in parallel with the normalisation of plasma gastrin levels.

Gastrin effects on isolated rat enterochromaffin-like cells following long-term hypergastrinaemia in vivo

The enterochromaffin-like (ECL) cells play an important role in the regulation of gastric acid secretion. They respond to gastrin by a prompt increase in histamine secretion, an effect which is mediated by the CCK-(B)/gastrin receptor acting through the IP(3)/DAG pathway. In the rat, long-term treatment with acid secretion inhibitors induces hypergastrinaemia which, in turn, results in ECL cell hypertrophy and hyperplasia. The aim of the present study was to evaluate various functional parameters in acutely isolated rat ECL cells, following long-term hypergastrinaemia in vivo. Rats were treated with vehicle or a supramaximal daily dose of omeprazole for more than 10 weeks to ensure ECL cell hyperplasia. ECL cells were isolated from vehicle-treated animals and 24, 72 and 120 h after the last dose of omeprazole. The functional activity of the acutely isolated ECL cells was determined by measuring gastrin-and forskolin-induced histamine secretion. Changes in cytosolic free calcium upon gastrin stimulation were monitored by digital video imaging. ECL cells successively regained their ability to respond to gastrin following long-term hypergastrinaemia, reaching close to vehicle-treated levels 120 h after the last dose of omeprazole. In the rat, the response pattern of the ECL cells appears to normalise in parallel with the normalisation of plasma gastrin levels.

Activation of mitogen-activated protein kinase subgroups and transcription factor in gastric epithelial cells by interleukin-1β

ECL cells successively regained their ability to respond to gastrin following long-term hypergastrinaemia, reaching levels close to control 120 hours after the last dose of omeprazole. In ECL ceils isolated 24 hours after the last dose of omeprazole, direct activation of adenylate cyclase by forskolin was unable to trigger histamine release, whilst the calcium response remained sensitive to higher gastrin concentrations. These results indicate that long-term hypergastrinaemia induces receptor desensitisation and post-receptor messenger modulation. The response pattem of ECL cells appears to normalise in parallel to the normalisation of plasma gastrin levels. Employees, Astra Hgssle AB, Mtilndal, Sweden.

Session 6: Is Hypergastrinaemia Dangerous to Man?

Achlorhydria has been discussed as a possibly dangerous consequence of therapeutic inhibition of gastric acid secretion since the introduction of H2-receptor antagonists. The risk of long-term hypergastrinaemia has only been considered for about 5 years. The reason for this was the demonstration that gastric carcinoids (ECLomas) observed after life-long treatment of rats with the proton pump inhibitor omeprazole could also be produced in rats by other methods leading to long-lasting profound hypergastrinaemia. Such methods were the 80% resection of the oxyntic mucosa or feeding of ranitidine (2000 mg/day) for 2 years. The endocrine tumours corresponded to the gastric carcinoids found in patients with long-lasting hypergastrinaemia due to pernicious anaemia or with a gastrinoma as part of the MEN I syndrome. Neither in animals nor in man could other endocrine tumours or adenocarcinomas of the gastrointestinal tract be related to hypergastrinaemia. Epidemiologic data do not support gastrin dependence of adenocarcinoma of the stomach or the colon. Experimental findings of gastrin effects on tumour growth in vivo and in vitro have been contradictory and may be explained by the presence of gastrin receptors on tumour cells and the role of gastrin as an autocrine growth factor in some of these tumours. Since acid blockade by proton pump inhibitors or H2-receptor blockers dose-dependently increase serum gastrin levels, patients with ranitidine-resistant peptic ulceration receiving long-term treatment with high-dose omeprazole have been followed up with serial gastric biopsy specimens for up to 5 years. Complete healing, moderate hypergastrinaemia, and a slight hyperplasia but no dysplasia of the ECL cells in the oxyntic mucosa have been observed, which seemed to be correlated to chronic gastritis progressing over the years. Despite these negative findings excessive hypergastrinaemia by overdosage of potent drugs for inhibition of gastric secretion should be avoided and monitoring of plasma gastrin levels is recommended in case of long-term treatment.

Inappropriate hypergastrinaemia in asymptomatic healthy subjects infected with Helicobacter pylori.

An ELISA test determined serologically that eight of 95 apparently healthy men (aged 19-26 years) had an asymptomatic infection with Helicobacter pylori at the time of simultaneous measurement of 24 hour intragastric acidity and 24 hour plasma gastrin concentration. There was no significant difference in the median integrated 24 hour intragastric acidity between the H. pylori positive and H. pylori negative subjects (688 and 842 mmol/h/l; p = 0.271, respectively), whereas the median integrated 24 hour plasma gastrin concentration was significantly higher in the H pylori positive than in the H pylori negative subjects (389 and 198 pmol/h/l; p less than 0.001). Longterm hypergastrinaemia, associated with persistent H pylori infection, could be a cause of the increased parietal cell mass that is considered characteristic of duodenal ulcer patients.

Gastrin and Gastric Enterochromaffin-like Cell Carcinoids in the Rat

Life-long administration (greater than or equal to 2 years) of a number of long-acting gastric acid inhibitors (including H2-receptor antagonists, omeprazole and ciprofibrate) has been associated with the development of gastric enterochromaffin-like cell (ECL cell) carcinoids in rats. It has been postulated that they are a consequence of some unique property of the longer-acting acid inhibitors. There is, however, a great deal of evidence to support the hypothesis that these gastric ECL cell carcinoids develop as a result of life-long hypergastrinaemia in rats. Several lines of investigation reported here show that gastric ECL cell hyperplasia occurs when gastrin levels are increased without the use of acid-inhibiting drugs. In rats, hypergastrinaemia developed after 4 weeks' administration of exogenous gastrin (4 micrograms/kg/h). The number of gastric ECL cells per visual field had increased to 250 compared with 180 in the controls. Long-term hypergastrinaemia, induced by partial gastric corpectomy, increased plasma gastrin levels from 200 to 800 pg/ml and the density of gastric ECL cells increased from 190 to 310 cells/visual field 10 weeks after the operation. Importantly, gastric ECL cell hyperplasia, which was produced in rats by administration of omeprazole, 14 mg/kg/day for 1 year, was fully reversible following normalization of gastrin levels. Until now, gastric ECL cell carcinoids have not been reported in studies of shorter-acting, reversible H2-receptor antagonists such as ranitidine, perhaps because the correct staining techniques (i.e. Grimelius and Sevier-Munger silver stains) have not been used.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of long-term hypergastrinaemia on the ultrastructure of enterochromaffin-like cells in the stomach of the rat, hamster and guinea pig

The present report describes the ultrastructure of the enterochromaffin-like (ECL) cells in the stomach of the rat, hamster and guinea pig, and the ultrastructural consequences of long-term hypergastrinaemia evoked either by continuous infusion of synthetic human (Leu15)-gastrin-17 for 4 weeks (rats) or by daily treatment with large doses of the antisecretory agent omeprazole for 2-10 weeks (rats, hamsters and guinea pigs). As a result, the ECL cells increased greatly in size (maximal effect after 2 weeks of omeprazole treatment, no further gain in size after 4 or 10 weeks). Also the endoplasmic reticulum and Golgi area were enlarged. The most conspicuous feature of the ECL cells is the cytoplasmic vesicles, which are of varying size and either devoid of a dense core or with a small, often eccentrically located dense core. The vesicles probably represent the main storage site of the secretory products of the ECL cell. In addition, the cytoplasm contains granules, which differ from the vesicles in that they possess a more or less electron-dense core, surrounded by a narrow halo. The size of the vesicles ranged from small to very large, while the granules were uniformly small. Many vesicles were seen to lie very close together, some displaying an irregular outline (vacuole-like vesicles), at times giving the impression that they were undergoing fusion. The profile size (median value) of the vesicles was unaffected by gastrin infusion for 4 weeks. However, there was a tendency to a relative increase in the number of very small vesicles. In contrast, the vesicles became larger during the omeprazole treatment. Also, the number of vesicles that seemed to be engaged in fusion increased after omeprazole treatment but not after gastrin infusion. The observations support the view that ECL cells are influenced by gastrin. The effects of gastrin infusion and of omeprazole treatment on ECL cell ultrastructure were not completely identical. It cannot be excluded that the omeprazole-evoked achlorhydria evokes effects unrelated to those of hypergastrinaemia on the ECL cells, or that endogenous gastrins may evoke effects that are in some ways distinct from those of synthetic human (Leu15)-gastrin-17. Alternatively, the additional effects seen after long-term omeprazole treatment may reflect simply the duration of the hypergastrinaemic stimulus.

Effect of intermittent weekend therapy with omeprazole on basal and bombesin- and pentagastrin-stimulated gastric acid and serum gastrin.

Omeprazole, a substituted benzimidazole inhibitor of the gastric H+/K+-ATPase, is a potent and long-acting antisecretory drug. Because of its high potency and because of the possible risk of long-term hypergastrinaemia intermittent therapy with this drug may be preferable to continuous treatment in patients requiring long-term treatment. We have therefore studied the effect of weekly 3-day courses of 20 mg/day omeprazole followed by a 4-day period without medication (weekend therapy) for 4 weeks on basal and bombesin- (150 ng/kg.h) and pentagastrin- (1.5 micrograms/kg.h) stimulated gastric acid secretion in 10 normal subjects. Gastric acid was measured in week 1, before (day 1) and immediately after the 3-day omeprazole course (day 4), and further on day 6 and day 8, immediately before the next course, and at similar intervals in week 4 (days 22, 25, 27, and 29). When compared with pretreatment values, basal and bombesin- and pentagastrin-stimulated gastric acid were significantly (p less than 0.01-p less than 0.05) inhibited on the days immediately after the courses (days 4 and 25) but were, except for a significant (p less than 0.05) reduction of pentagastrin-stimulated gastric acid on day 8, not significantly affected on all other days. Basal and integrated bombesin-stimulated serum gastrin values were not significantly changed, whereas bombesin-stimulated peak serum gastrin was significantly (p less than 0.05) increased on days 22 and 29. Since this schedule of omeprazole induces pronounced, but transient, inhibition of gastric acid secretion without provoking marked hypergastrinaemia, intermittent weekend therapy may be suitable for long-term maintenance treatment with this drug.

Activation and hyperplasia of gastrin and enterochromaffin-like cells in the stomach.

The stomach is rich in endocrine cells, most of which are still unidentified with respect to the peptide hormones they produce. The endocrine cell populations in the antrum usually differ from those in the oxyntic mucosa. Gastrin cells are found in the antrum and respond readily to stimuli from the gastric lumen, such as changes in the pH and the presence of food. In order to study the functional control of the antral gastrin cell, rats were subjected to different kinds of surgery. The serum gastrin concentrations in the various experimental groups were measured 8-10 weeks after the operations. Elevated antral pH raised the serum gastrin concentration. The combination of elevated antral pH and the passage of food over the pyloric glands produced gastrin cell hyperplasia. The operation that was most effective in inducing gastrin cell hyperplasia was removal of the acid-producing part of the stomach. Interestingly, gastrin cell hyperplasia was seen also after bilateral truncal vagotomy, indicating that an intact vagal innervation is not essential for the development of gastrin cell hyperplasia. Enterochromaffin-like (ECL) cells are endocrine/paracrine cells that are numerous in the acid-producing part of the stomach in many species. In the rat, they occur predominantly in the basal half of the oxyntic mucosa and produce and store histamine. The ECL cells have an unknown function and do not seem to respond to stimuli from the gastric lumen. They are activated by circulating gastrin and by vagal excitation. Gastrin mobilises histamine from these cells and activates the histamine-forming enzyme, histidine decarboxylase. Long-term hypergastrinaemia produces diffuse ECL cell hyperplasia, whereas hypogastrinaemia (following removal of the endogenous stores of gastrin by antrectomy) reduces the ECL cell number. Portacaval shunt brings about a marked increase in the number of ECL cells through an unknown mechanism. Also neuronal stimuli are important for the trophic control of the ECL cells. Studies of unilaterally vagotomised rats showed reduced weight and thickness of the oxyntic mucosa as well as a markedly reduced number of ECL cells on the denervated side. Gastric carcinoids in man are rare tumours predominantly made up of ECL cells. The incidence of such tumours is increased in patients with hypergastrinaemia (pernicious anaemia, Zollinger-Ellison syndrome). A diffuse ECL cell hyperplasia is a common finding in such patients, which is in keeping with the known gastrin sensitivity of the normal ECL cell in the rat.