Is pentagastrin-stimulated secretion mediated by histamine?

Skeletal effects of a gastrin receptor antagonist in H+/K+ATPase beta subunit KO mice

Epidemiological studies suggest an increased fracture risk in patients taking proton pump inhibitors (PPIs) for long term. The underlying mechanism, however, has been disputed. By binding to the gastric proton pump, PPIs inhibit gastric acid secretion. We have previously shown that proton pump (H(+)/K(+)ATPase beta subunit) KO mice exhibit reduced bone mineral density (BMD) and inferior bone strength compared with WT mice. Patients using PPIs as well as these KO mice exhibit gastric hypoacidity, and subsequently increased serum concentrations of the hormone gastrin. In this study, we wanted to examine whether inhibition of the gastrin/CCK2 receptor influences bone quality in these mice. KO and WT mice were given either the gastrin/CCK2 receptor antagonist netazepide dissolved in polyethylene glycol (PEG) or only PEG for 1year. We found significantly lower bone mineral content and BMD, as well as inferior bone microarchitecture in KO mice compared with WT. Biomechanical properties by three-point bending test also proved inferior in KO mice. KO mice receiving netazepide exhibited significantly higher cortical thickness, cortical area fraction, trabecular thickness and trabecular BMD by micro-CT compared with the control group. Three-point bending test also showed higher Young's modulus of elasticity in the netazepide KO group compared with control mice. In conclusion, we observed that the gastrin receptor antagonist netazepide slightly improved bone quality in this mouse model, suggesting that hypergastrinemia may contribute to deteriorated bone quality during acid inhibition.

The regulation of histidine decarboxylase gene expression

Histamine is a biogenic amine, which is involved in a variety of biologic processes comprising inflammation, allergic responses, neurotransmission and regulation of gastric acid secretion. The key enzyme for the generation of histamine is histidine decarboxylase (HDC), which converts the amino acid L-histidine to histamine. In this article, we review the history, biochemistry and molecular biology of this enzyme. Northern blot studies in rats demonstrated that HDC gene expression in the stomach and liver are developmentally regulated with highest levels of expression in the late fetal state, indicating a role of the gene in growth and development. In the stomach of adult rats, HDC mRNA levels are elevated after omeprazole-induced hypergastrinemia, and in situ hybridization showed that expression of HDC is restricted to the glandular area in which ECL cells are located. Since no permanent ECL cell line is at hand for in vitro studies, we established a suitable cell system by stable transfection of a human gastric adenocarcinoma cell line (AGS) with the CCK-B/gastrin receptor. Transfection of this AGS-B cell line with reporter gene constructs comprising 5'-flanking DNA sequence of the HDC gene joined to the firefly luciferase gene revealed transcriptional regulation of the HDC promoter by gastrin through a protein-kinase C-dependent pathway. Taken together, these studies are consistent with the concept of HDC transcriptional regulation as at least one phase of the overall response to gastrin.

Inhibitory effect of DS-4574, a mast cell stabilizer with peptidoleukotriene receptor antagonism, on gastric acid secretion in rats

We examined the inhibitory effect of DS-4574 (6-(2-cyclohexylethyl)[1,3,4]thiadiazolo[3,2-alpha]-1,2,3- triazolo[4,5-d] pyrimidin-9(3H)-one), a mast cell stabilizer with peptidoleukotriene receptor antagonism, on gastric acid secretion stimulated by several secretagogues in rats. In anesthetized rats with acute gastric fistulas, DS-4574 (50 mg/kg, intraduodenal) significantly inhibited gastric acid secretion induced by both carbachol (50 micrograms/kg, s.c.) and pentagastrin (75 micrograms/kg, s.c.) but not by histamine (2.5 mg/kg, s.c.). In unanesthetized pylorus-ligated rats, DS-4574 (10 and 25 mg/kg, intraduodenal) markedly suppressed increases in gastric acid output and histamine leakage into the gastric juice produced by carbachol (0.1 mg/kg, s.c.) or pentagastrin (1 mg/kg, s.c.). When the relationship between acid output and histamine leakage elicited by carbachol and pentagastrin was assessed, there was a close correlation (r = 0.84) that was highly significant (P < 0.01). In the in vitro study with rat gastric tissues, DS-4574 (10(-7)-10(-5) M) had no effect on the K(+)-dependent ATPase activity or on aminopyrine uptake into mucosal preparations containing parietal cells stimulated by carbachol (10(-5) M), histamine (10(-4) M), or dibutyryl-cyclic AMP (10(-3) M). These results suggest that the effect of DS-4574 may be mediated by inhibition of endogenous histamine from histamine-storing cells in the stomach.

In man histamine and muscarinergic mechanisms are essential mediators of acid secretion in response to synthetic human gastrin (1-17)

It is still controversial whether gastrin stimulates acid secretion by interacting with specific gastrin receptors on parietal cells or via endogenous mediators, e.g., histamine. Therefore, it was our aim to determine in healthy human volunteers (n = 14; 3 females, 11 males; age 23-28 years) the degree by which the specific histamine H2-receptor antagonist famotidine or the muscarinergic antagonist atropine block acid secretion in response to synthetic human gastrin (hG) (1-17). Famotidine was deliberately administered at a supramaximal dose (40 mg i.v. bolus) to reliably block any and all effects of endogenous histamine on the parietal cells. After an overnight fast famotidine or saline were injected i.v., and gastric secretions were collected via a nasogastric tube for the ensuing 60 min to assess basal secretion. Thereafter, hG (1-17) was infused for 60 min in randomized order at two different rates: 0.75 ng/kg/min resulting in postprandial plasma gastrin levels (55-66 pg/ml), and 1.5 ng/kg/min yielding supraphysiologic levels (110-136 pg/ml). Both rates increased basal acid secretion (meq/10 min) from 0.5 +/- 0.2 to 3.8 +/- 0.6 and 4.7 +/- 0.5, respectively. Famotidine abolished basal acid secretion and completely blocked acid and volume secretion in response to both hG (1-17) doses. After injection of famotidine both hG (1-17) doses resulted in plasma levels exceeding those in controls by 18-27 pg/ml. A similar increase (14-16 pg/ml) was observed after famotidine injection without simultaneous hG (1-17) infusion indicating that this increase was due to the release of endogenous gastrin when the acid feedback inhibition was blocked by famotidine. To study a potential additional role of cholinergic mechanisms the effect of atropine (7 micrograms/kg i.m.) on hG (1-17)-induced acid secretion was examined. Atropine reduced basal acid secretion from 0.8 +/- 0.1 to 0.1 +/- 0.08 meq/15 min. Similarly, the response to 0.75 ng/kg/min hG (1-17) was reduced by 72.9%. Basal gastrin release was not altered by atropine which, however, tended to increase serum gastrin levels during infusion of hG (1-17) by 16-24 pg/ml. We conclude that in man histamine and muscarinic mechanisms are essential mediators of gastrin-stimulated acid secretion. The present data argue against a significant direct effect of gastrin alone on human parietal cells but rather support potentiating interaction with histamine and cholinergic mechanisms.

Argyrophil cells, mast cells, and histamine in the fundic mucosa of antrectomized patients

Fasting gastrinemia, fundic argyrophil cell density, mast cell number, basal fundic histamine content and histidine decarboxylase activity were determined in 20 antrectomized patients and 20 control subjects. Fasting gastrinemia and fundic argyrophil cell density were significantly lower in antrectomized patients than in controls, whereas fundic mast cell number, basal histamine content, and histidine decarboxylase activity did not differ significantly between the two groups. In antrectomized patients the basal fundic histamine content appears related to the fundic mast cell number, as a consequence of the reduced effect of gastrin on argyrophil cells.

Studies of isolated parietal and enterochromaffin-like cells from the rat

Rat gastric mucosal cells isolated by enzyme dispersion were separated by elutriation centrifugation. The amount of histamine and the number of enterochromaffin-like (ECL) cells and parietal cells were determined in the crude mucosal cells and the various elutriation fractions. The mucosal cells contained 2.6% ECL and 20% parietal cells. Elutriation centrifugation resulted in good separation of parietal cells and ECL cells. Most of the ECL cells were elutriated in the small cell fractions. Scattered ECL cells were also present in the fraction enriched with parietal cells. Histamine and carbacholine stimulated aminopyrine uptake in a concentration-dependent manner with about the same efficacy, 5.6 times the base-line value. When combined with the phosphodiesterase inhibitor isobutyl methylxanthine, the maximal histamine stimulation was increased to 16.8 times the base-line value, and the sensitivity increased about 10-fold. Gastrin at high and unphysiologic concentrations stimulated only faintly the aminopyrine uptake in parietal cells and the histamine release from ECL cells.

Histamine concentration of gastric mucosa in Helicobacter pylori positive and negative children

The histamine concentration was determined by enzymatic isotopic method in biopsy specimens of oxyntic mucosa from 37 children. Nineteen of the 37 had Helicobacter pylori associated gastritis (9 with duodenal ulcer). The histamine concentration in the H pylori negative group was mean (SD) 54.1 (23.1) micrograms/g fresh weight, and that in the H pylori positive group was 26.3 (14.2) micrograms/g (p less than 0.01). There was also a significant difference between H pylori positive patients with duodenal ulcer (19.8 (6.3) micrograms/g) and those without ulcer (31.4 (17.9) micrograms/g) (p less than 0.05). These results suggest that H pylori positive patients, especially those with duodenal ulcer, have reduced 'stored' histamine, perhaps because of increased histamine liberation.

Gastrin-histamine interactions: direct and paracrine elements

The receptors mediating the physiologic actions of gastrin on acid secretion and growth have thus far not been localized to specific cells or fully characterized. Studies in canine fundic mucosa indicate that gastrin receptors are present on several cell types, including parietal cells and somatostatin cells. There is also increasing evidence for a gastrin-inducible pool of histamine in the fundic mucosa which is presumably stored in histamine-enterochromaffin-like cells. From the vantage point of studies in the canine fundic mucosa, the issue is no longer which cell type has the gastrin receptor but to sort out the mechanisms by which the effects of the gastrin receptors on endocrine/paracrine (histamine and somatostatin) cells and exocrine (parietal) cells are integrated to regulate secretory function and mucosal growth and differentiation.

In vivo catabolism of histamine in the human stomach

The importance of the stomach in the magnitude of excreted amounts of the major histamine metabolite in the urine was studied during total parenteral nutrition in five patients before and after total gastrectomy. In all subjects, a reduction in the 24-h urinary excretion of methylimidazoleacetic acid was observed. No corresponding effect was seen after an operation because of abdominal aortic aneurysm. In patients with duodenal ulcer disease and those submitted to a cholecystectomy because of cholecystolithiasis, we studied the catabolism of histamine in the stomach by injecting 14C-histamine directly into the portal vein and, simultaneously, 3H-histamine intra-arterially to the corpus fundus region of the stomach and subsequently determining the urinary excretion of 14C. 3H-histamine and their basic and acid metabolites, respectively. We found no apparent difference in the pattern of excreted 14C and 3H metabolites between the two patients groups, indicating that the catabolism of histamine in the stomach of patients with duodenal ulcer disease is similar to that in 'healthy' controls.

Histamine metabolism in human gastric mucosa. Effect of pentagastrin stimulation

The metabolism of histamine in the human gastric mucosa was studied in the basal state and during pentagastrin stimulation. Studies were made in healthy volunteers and in patients with peptic ulcer disease. Mucosal biopsies were taken from antral and oxyntic gland areas whereupon histamine content, histidine decarboxylase activity, and histamine methyltransferase activity were simultaneously assayed. Histamine content of the oxyntic gland mucosa was decreased as a consequence of pentagastrin administration in all groups studied, and this decrease was numerically largest in patients with duodenal ulcer disease. Pentagastrin induced a significant increase in histidine decarboxylase activity of the oxyntic gland mucosa with the most profound increase seen in patients with duodenal ulcer. The highest rates of histamine formation were present in the oxyntic mucosa of patients with Zollinger-Ellison syndrome. The activity of histamine methyltransferase was the same in all groups studied and was not changed by pentagastrin. In conclusion, pentagastrin administration in humans is followed by a significant mobilization of histamine only from the oxyntic gland mucosa, an effect that is more pronounced in patients with duodenal ulcer disease.

Histamine and duodenal ulceration in renal transplant recipients

Six of 25 renal transplant recipients had a duodenal ulcer at endoscopy. Histamine concentration and the activity of histamine methyltransferase, the degrading enzyme of histamine, were measured in gastric mucosal biopsies obtained at endoscopy and compared with patients with duodenal ulcer but not undergoing transplant and with patients with an apparently normal stomach and duodenum. Histamine concentrations in the corpus (no ulcer, median: 151 nmol/g; DU, median: 122 nmol/g) and in the antrum (no ulcer, median: 118 nmol/g; with DU, median: 113 nmol/g) of renal transplant patients, irrespective of ulcer diagnosis, and in patients with a chronic duodenal ulcer (median corpus histamine: 137 nmol/g and median antral histamine: 126 nmol/g) were not different from one another but significantly lower than the corresponding values in normal subjects (median corpus histamine: 241 nmol/g, p less than 0.01, and median antral histamine: 178 nmol/g, p less than 0.05). Histamine concentration in the corpus was significantly higher than in the antrum in all three groups of patients (p less than 0.05). There were no significant differences in histamine methyltransferase activity in any of the groups studied. Mucosal histamine and histamine methyltransferase activity were significantly correlated in the corpus (p less than 0.05) and antrum (p less than 0.02). Plasma concentration of histamine after transplant was higher in the patients who subsequently were discovered to have a duodenal ulcer (p less than 0.05). The occurrence of ulcer after transplantation was not related to the serum creatinine level. The uniform depletion of gastric histamine and increase in circulatory histamine after renal transplantation may be a factor in the pathogenesis of duodenal ulcer disease in this clinical situation.

First-degree atrioventricular block in a young duodenal ulcer patient treated with a standard oral dose of ranitidine

A 20-year-old male patient on oral treatment with ranitidine 300 mg/day in a single bedtime dose was admitted to hospital for a brief episode of syncope which had occurred 20 min earlier. All clinical, laboratory and instrumental examinations yielded negative findings, except for electrocardiographic evidence of first-degree atrioventricular block. Administration of atropine produced transient disappearance of the block, which disappeared altogether after discontinuing ranitidine treatment. Two separate rechallenges with ranitidine each produced recurrence of (asymptomatic) first-degree atrioventricular block at electrocardiographic examination, but oral treatment with cimetidine (400-800 mg/day) and famotidine (40-80 mg/day) induced no electrocardiographic abnormalities. The hypothesis that this patient may be abnormally susceptible to the cholinergic or cholinergic-like effect of ranitidine, a side effect unrelated to the drug's primary H2-blocking action, would appear to be consistent with evidence of an increased vagal tone of the atrioventricular node as revealed by atrial pacing. However, the ability of ranitidine to release histamine in man and the potential dysrhythmia-inducing effect of histamine should also be taken into consideration.

Cyclic AMP in gastric juice does not reflect histamine H2 receptor activity in Heidenhain pouch dog

It is strongly believed that cAMP mediates histamine H2 receptor activity, but does not mediate gastrin and acetylcholine stimulation of gastric acid secretion. Therefore, cAMP production could be a marker of H2 receptor activity. Whether endogenous histamine mediates gastrin and/or acetylcholine stimulation, at least partially, remains to be elucidated. If cAMP in the gastric juice reflects H2 receptor activity, we can investigate whether endogenous histamine mediates gastrin and/or acetylcholine stimulation in vivo. In this study, we investigated whether cAMP in the gastric juice reflected histamine H2 receptor activity in the Heidenhain pouch dog in vivo using different kinds of inhibitors of gastric secretion. Our hypothesis was as follows: Upon betazole stimulation, cimetidine, an H2 receptor antagonist, should decrease cAMP output into the gastric juice, but omeprazole, an H+, K+-ATPase blocker, should not, because it blocks at a site more peripheral than the H2 receptor and the production of cAMP. Sixty minutes after betazole administration, 4.0 mumol/kg of cimetidine and 0.18 mumol/kg omeprazole were administered intravenously and they inhibited gastric juice volume to a similar degree, that is, 49.6% and 52.1%, respectively. However, omeprazole caused a greater decrease in cAMP output than cimetidine. Inhibition with 4 mumol/kg/h of cimetidine or 0.2 mumol/kg of omeprazole from the beginning of betazole stimulation also caused similar decreases in gastric juice volume, 66.6% and 60.6%, respectively. Both inhibitors decreased cAMP output into the gastric juice in a similar fashion in the first two 30 minute periods. These results do not agree with our hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Histamine and duodenal ulcer: effect of omeprazole on gastric histamine in patients with duodenal ulcer

Gastric mucosal concentrations of histamine and of its metabolic enzyme, histamine methyltransferase activity, were measured in patients with duodenal ulcer disease and patients with an apparently normal stomach and duodenum. Patients with duodenal ulcer had significantly less (p less than 0.05) mucosal histamine (median 204 nmol/g) than control subjects (median 252 nmol/g). There was no significant difference between the two groups in their histamine methyltransferase activity values. Omeprazole therapy did not significantly change mucosal histamine (+23%), histamine methyltransferase activity (+5%), histamine release before (+5%) or during (+7%) pentagastrin infusion. It significantly decreased acid secretion during pentagastrin stimulation (median -73%, p less than 0.001). Omeprazole, like cimetidine, does not stop histamine release during pentagastrin stimulation.

Effects of a mast cell stabiliser (FPL 52694) on human gastric secretion

The effects of a new monochrome mast cell stabilizer (FPL 52694) on gastric secretion have been studied in healthy volunteers. When administered orally for 3 days, FPL 52694 consistently reduced nocturnal and pentagastrin-stimulated secretion of acid by about 50%. Meal-stimulated gastric secretion was not affected by the drug. Inhibition of the gastric secretory response to pentagastrin was not significant when single doses of the drug were administered either into the stomach or the duodenum, but administration of multiple doses resulted in significant inhibition. The drug does not inhibit gastric secretion by injuring the gastric mucosa, since the gastric mucosal barrier to back diffusion of hydrogen ions is not affected. We conclude that this mast cell stabilizer provides an interesting tool for studying aspects of the physiological control of gastric secretion and may have a therapeutic role in peptic ulceration.