Gastrin produces an immediate and dose-dependent histamine release preceding acid secretion in the totally isolated, vascularly perfused rat stomach

Review article: the use of gastric acid-inhibitory drugs--physiological and pathophysiological considerations

All vertebrates secrete gastric acid. Acid denatures the proteins in the food and thus makes them more accessible to proteolytic enzymes, and it kills swallowed micro-organisms. Gastric acid plays an important pathogenetic role in peptic ulcer disease and reflux oesophagitis. In these diseases, drugs that inhibit secretion of gastric acid will heal the lesions and suppress the symptoms. However, both reflux oesophagitis and peptic ulcer tend to recur when the acid-inhibitory treatment is stopped. Therefore, these patients often require long-term treatment with acid-inhibitors. In this overview the potential risks of long-term profound inhibition of acid secretion, raising the pH above 4 for a considerable time, resulting in reduced killing of micro-organisms and secondary hypergastrinaemia, are discussed. Gastrin regulates both the function (production and release of histamine) and growth of the enterochromaffin-like (ECL) cell. Hitherto, the role that this cell plays in gastric carcinogenesis appears to have been underestimated.

Somatostatin inhibits gastrin-induced histamine secretion and synthesis in the rat

Somatostatin is a potent inhibitor of gastric acid secretion. However, the effect of somatostatin on gastric histamine secretion and synthesis has not been well understood, despite the fact that histamine plays a key role in the regulation of gastric acid secretion. This study was designed to determine the effect of somatostatin on gastric histamine mobilization and acid secretion in conscious rats. In conscious rats with a gastric fistula, a 4 h intravenous infusion of gastrin-17 I (1 nmol/kg/h) evoked a marked increase in fundic histidine decarboxylase activity (the sole histamine-forming enzyme) and reduced fundic histamine content with a concomitant increase in gastric acid secretion. Somatostatin-14 (10 nmol/kg/h) significantly inhibited gastrin-induced gastric acid secretion and fundic histidine decarboxylase activity and prevented a gastrin-induced decrease in fundic histamine content. In conscious rats with a vesical fistula, somatostatin-14 (10 nmol/kg/h) significantly inhibited the urinary histamine excretion induced by a gastrin-17 I (1 nmol/kg/h) infusion. These findings suggest that the inhibitory action of somatostatin on gastrin-induced acid secretion is mediated by the inhibition of histamine mobilization.

Histamine secretion from rat enterochromaffinlike cells

BACKGROUND

In vivo studies have suggested an important role for gastric enterochromaffinlike (ECL) cells in mediating acid secretion. Direct evidence for this function is lacking and requires a preparation of highly purified ECL cells. This work investigates the possible role and mechanism of histamine release from the ECL cell in the peripheral regulation of acid secretion, using purified ECL cells from rat fundic mucosa.

METHODS

A combination of elutriation and density-gradient centrifugation was used to purify rat fundic ECL cells. Enrichment was determined by the presence of acidic vacuoles containing a V type adenosine triphosphatase, electron microscopy, immunostaining, and histamine content and release.

RESULTS

ECL cells were enriched at least 65-fold with respect to the fundic epithelium. Gastrin (EC50 0.2 nmol/L) and cholecystokinin octapeptide (nonsulfated, EC50 0.04 nmol/L) stimulated histamine release in a time- and dose-dependent manner, suggesting a CCK-B receptor subtype, confirmed by the inhibition of gastrin/CCK stimulation with the CCK-B antagonist L365,260. Somatostatin also inhibited gastrin-mediated histamine release. Single cell imaging showed that gastrin elevated intracellular cytosolic calcium concentration biphasically. Carbachol and the C kinase activator 120-tetradecanoylphorbol-13-acetate also stimulated histamine release. Epinephrine (blocked by propranolol), forskolin, and dibutyryl-5'-cyclic adenosine monophosphate were also effective, implicating a beta-adrenergic pathway. The H3 agonist R-alpha-methyl-histamine inhibited, whereas the H3-antagonist thioperamide potentiated gastrin/CCK stimulated histamine release.

CONCLUSIONS

These in vitro results support a central role for the ECL cell in the peripheral regulation of gastric acid secretion.

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.

Mechanism by which histamine increases gastric mucosal blood flow in the rat. Role of luminal H+

The mechanism by which histamine increases gastric mucosal blood flow (GMBF) was investigated in the anesthetized rat. The experiment was performed in the presence of tripelennamine, an H1 antagonist, to focus on the relationship between acid secretion (H2-receptor-mediated response) and GMBF. The stomach was mounted on a Lucite chamber, perfused with saline, and GMBF was measured by laser Doppler flowmetry simultaneously with acid secretion. Under these conditions, histamine at the submaximal dose significantly increased GMBF as well as acid secretion, and this increase of GMBF was completely blocked when acid secretion was inhibited by cimetidine or omeprazole. The elevation of GMBF caused by histamine was also significantly attenuated when luminal H+ was removed by intraluminal perfusion with NaHCO3 or glycine. Glycine by itself did not affect the increase of acid secretion induced by histamine and the increase of GMBF caused by isoproterenol, yet significantly inhibited the GMBF response induced by pentagastrin. Intraluminal perfusion with HCl also produced an increase of GMBF in a concentration-related manner, even in the presence of omeprazole during histamine infusion. Pretreatment of the animals with indomethacin significantly blocked the GMBF responses induced by either histamine or luminal HCl. These results suggest that the increase of GMBF during acid secretion induced by histamine may be caused by luminal H+ and involve endogenous prostaglandins in its mechanism.

Effects of carbachol and gastrin on 14C-aminopyrine accumulated in rabbit gastric glands and cells

The present study examines the possible existence of a mechanism regulating emptying of the secretory canaliculi content of the parietal cell and the possible effects of carbachol and gastrin on such a mechanism. In rabbit gastric glands stimulated with carbachol, 14C-aminopyrine accumulation reached a maximum after 15 min and then started to decrease. This decrease was not accompanied by a decrease in oxygen consumption, nor was any decrease of accumulated 14C-aminopyrine seen in dispersed gastric cells. In glands but not in cells stimulated with histamine together with 3-isobutyl-1-methylxanthine (IMX), carbachol induced a reduction in the accumulated 14C-aminopyrine content, whereas the effect of gastrin was less pronounced. The carbachol-induced reduction was counteracted by atropine but was not accompanied by a decrease in oxygen consumption. It is suggested that there exists a mechanism that controls the emptying of the secretory canaliculi content of the parietal cell, and that carbachol, in addition to stimulating acid production, also contributes to this emptying. Paracrine factors may be involved in this latter mechanism.

Food stimulation of histidine decarboxylase messenger RNA abundance in rat gastric fundus

1. Histidine decarboxylase in the enterochromaffin-like cells of the gastric corpus mucosa converts histidine to histamine which in turn stimulates gastric acid secretion. The control of histidine decarboxylase activity is poorly understood. We have examined how fasting and refeeding influence the abundance of the messenger RNA encoding histidine decarboxylase in the gastric corpus of the rat. 2. The polymerase chain reaction was used to generate a probe for detection of histidine decarboxylase messenger RNA in Northern and slot blots of total RNA from the gastric corpus of rats fasted for up to 48 h, or fasted and then refed. A gastrin monoclonal antibody was used to neutralize the action of endogenous gastrin. 3. Fasting progressively reduced histidine decarboxylase messenger RNA abundance by 3- to 4-fold after 48 h. Refeeding induced a rapid increase in histidine decarboxylase messenger RNA abundance which was detectable after 30 min. 4. There was a significant correlation between histidine decarboxylase messenger RNA abundance and plasma gastrin. Administration of gastrin antibody inhibited the increase in histidine decarboxylase activity after 6 h refeeding, but not after refeeding for 30 min. 5. The results suggest that histamine-mediated changes in postprandial acid secretion depend on control of histidine decarboxylase mRNA levels, and that gastrin regulates production of this enzyme in the rat over periods of a few hours.

Enterochromaffin-like (ECL) cells and their growths: relationships to gastrin, reduced acid secretion and gastritis

ECL cells are argyrophilic endocrine cells of the stomach. Their distribution is species specific, however they are consistently located in the oxyntic mucosa and, in particular, in very close contact with the adenomeres of acidopeptic glands. ECL cells store histamine and are considered a key element in the mechanisms of gastric acid secretion as controlled by gastrin stimulus. Their peculiar anatomical disposition and secretory properties strongly suggest that ECL cells exert their function by a paracrine mechanism, i.e. by releasing histamine in the extracellular spaces surrounding acid-producing parietal cells. ECL cell activity is strongly stimulated by gastrin, which, once applied as a long-standing stimulus, also exerts a potent proliferating effect. Long-lasting hypergastrinaemia has been demonstrated to elicit ECL cell proliferation in laboratory animals, inducing ECL cell hyperplasia, dysplasia and ECL cell tumours, i.e. argyrophilic gastric carcinoids. However, in experimental rodents it is believed that hypergastrinaemia is not per se a stimulus capable of inducing ECL cell transformation, a predisposing genetic background being required for tumour development in endocrine organs. In man, long-standing hypergastrinaemia exerts the same proliferative pressure on ECL cells and is associated with hyperplasia with or without dysplastic changes and carcinoid development. Clinical evidence suggests that other factors, both genetic and environmental, are required to induce ECL cell transformation and carcinoid development. For this reason human gastric argyrophilic ECL carcinoids are subdivided into three main groups depending on their clinical background: (1) gastric carcinoids in patients with chronic atrophic gastritis; (2) gastric carcinoids in patients with Zollinger-Ellison and multiple endocrine neoplasia type 1 syndrome (MEN-ZES); and (3) solitary, sporadic gastric carcinoids. The clinical assessment of carcinoid-bearing patients is strongly recommended for better diagnosis and management of patients.

Pharmacology of gastric acid inhibition

Gastric acid secretion is precisely regulated by neural (acetylcholine), hormonal (gastrin), and paracrine (histamine; somatostatin) mechanisms. The stimulatory effect of acetylcholine and gastrin is mediated via increase in cytosolic calcium, whereas that of histamine is mediated via activation of adenylate cyclase and generation of cAMP. Potentiation between histamine and either gastrin or acetylcholine may reflect postreceptor interaction between the distinct pathways and/or the ability of gastrin and acetylcholine to release histamine from mucosal ECL cells. The prime inhibitor of acid secretion is somatostatin. Its inhibitory paracrine effect is mediated predominantly by receptors coupled via guanine nucleotide binding proteins to inhibition of adenylate cyclase activity. All the pathways converge on and modulate the activity of the luminal enzyme, H+,K(+)-ATPase, the proton pump of the parietal cell. Precise information on the mechanisms involved in gastric acid secretion and the identification of specific receptor subtypes has led to the development of potent drugs capable of inhibiting acid secretion. These include competitive antagonists that interact with stimulatory receptors (e.g. muscarinic M1-receptor antagonists and histamine H2-receptor antagonists) as well as non-competitive inhibitors of H+,K(+)-ATPase (e.g. omeprazole). The histamine H2-receptor antagonists (cimetidine, ranitidine, famotidine, nizatidine and roxatidine acetate) continue as first-line therapy for peptic ulcer disease and are effective in preventing relapse. Although they are generally well tolerated, histamine H2-receptor antagonists may cause untoward CNS, cardiac and endocrine effects, as well as interfering with the absorption, metabolism and elimination of various drugs. The dominance of the histamine H2-receptor antagonists is now being challenged by omeprazole. Omeprazole reaches the parietal cell via the bloodstream, diffuses through the cytoplasm and becomes activated and trapped as a sulfenamide in the acidic canaliculus of the parietal cell. Here, it covalently binds to H+,K(+)-ATPase, the hydrogen pump of the parietal cell, thereby irreversibly blocking acid secretion in response to all modes of stimulation. The main potential drawback to its use is its extreme potency which sometimes leads to virtual anacidity, gastrin cell hyperplasia, hypergastrinaemia and, in rats, to the development of carcinoid tumours. The cholinergic receptor on the parietal cell has recently been identified as an M3 subtype and that on postganglionic intramural neurones of the submucosal plexus as an M1 subtype.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurohormonal regulation of histamine release from isolated rabbit fundic mucosal cells

Histamine-containing cells isolated from rabbit fundic mucosa were found in a small cell elutriation fraction (cells with diameter about 9-12 microns) enriched in mucus and endocrine cells and containing less than 1% mast cells (F1 cells). Gastrin (HG-17), pentagastrin and CCK-8 (C-terminal octapeptide of cholecystokinin) dose-dependently stimulated histamine release (EC50, respectively, 0.126 +/- 0.03, 0.92 +/- 0.15 and 0.211 +/- 0.025 nM) and somatostatin inhibited this release. PGE1, PGE2 and PGD2 alone were unable to enhance histamine release even at high concentrations but, when used in combination with gastrin of CCK-8, the release of histamine caused by these peptides was potentiated (about 1.5- to 2-fold). Carbachol also enhanced the liberation of histamine but with a weaker potency and efficacy than the gastrointestinal peptides (EC50: 1.50 +/- 0.06 microM). The use of specific muscarinic antagonists for M1-, M2- and M3-type receptors led us to conclude that an M1 receptor might be involved in the muscarinic-induced stimulation of histamine release. Activators of protein kinase C, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1-oleyl-2-acetyl-glycerol (OAG) as well as the calcium ionophore, A23187, induced histamine release, whereas agents which increased intracellular cAMP content were devoid of effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct gastrin action on isolated rat parietal cells induces morphological transformations

In isolated rat parietal cells, a potentiating effect by gastrin of the stimulatory action of histamine and dibutyryl-cAMP (DBcAMP) on aminopyrine accumulation, an index of the acid formed and trapped by the cells, was recently reported by us (1991, Am. J. Physiol. 261, G621-G627). In the present study, this mechanism of action of gastrin was further investigated. Enriched parietal cells (approximately 65% parietal cells) were incubated under different conditions and processed for electron microscopy. Morphometric analysis of the micrographs revealed that pentagastrin (100 nM) was as efficient as histamine (100 microM) in inducing the formation of vacuolar/canalicular spaces in the parietal cells. In the presence of the histamine H2-receptor antagonist ranitidine, histamine was ineffective but pentagastrin and gastrin-17 (G17) maintained their capacity to induce the morphological transformations. By stimulation with pentagastrin plus histamine, the vacuolar/canalicular volume was 2-fold higher than by stimulation separately with each one of the secretagogues. G-17 (100 nM) alone was ineffective but potentiated the maximal [14C]aminopyrine accumulation obtained with 100 microM histamine in mucosal cells (approximately 25-35% parietal cells). Ranitidine blocked both histamine-and histamine plus G-17-stimulated aminopyrine accumulation. G-17 potentiated also the stimulation by 1 mM dibutyryl-cyclic AMP but this was not inhibited by ranitidine. Pentagastrin (100 nM) increased the basal [14C]glucose oxidation in mucosal cells by 30%. This increase was not blocked by ranitidine which, however, abolished the histamine-stimulated glucose oxidation. Incubation of the cells with pentagastrin plus histamine resulted in a glucose oxidation which equaled the sum of the values obtained by each one of the agents. These results indicate that gastrin, acting directly on the parietal cells, potentiates the action of histamine on aminopyrine accumulation by increasing the vacuolar/canalicular spaces, a process that is reflected in the metabolic activity of the cells. Thus a major effect of gastrin at the parietal cell level appears to be the induction of a morphology which is characteristic of stimulated cells rather than a direct activation of ion-transport mechanisms.

Effects of H1-receptor antagonists on 14C-aminopyrine accumulated in histamine-stimulated rabbit gastric glands

After stimulation of gastric acid production there is a considerable delay before the acid starts to appear in the gastric lumen. The present study was carried out on isolated gastric glands to test the hypothesis that there may be a mechanism in the parietal cell that contributes to this delay by preventing emptying of the secretory canaliculi. Glands were incubated with 14C-aminopyrine and stimulated with histamine. After accumulation of 14C-aminopyrine various concentrations of H1-receptor antagonists were added. Clemastine, promethazine, and hydroxyzine effectively and cetirizine and tripelennamine less effectively decreased the accumulated 14C-aminopyrine content in a dose-dependent manner without significantly reducing the oxygen consumption. The H1-receptor antagonists influenced the 14C-aminopyrine content in another manner than H2-receptor antagonists. No effects were obtained by atropine or lidocaine, indicating that the elimination of 14C-aminopyrine is not an anticholinergic effect or due to membrane effects as exerted by local anesthetics. Stimulation of glands by further addition of histamine did not significantly stimulate the uptake of 14C-aminopyrine in the glands, whereas stimulation with db-cAMP produced an increase that was most pronounced when low concentrations of hydroxyzine had been used. It is suggested that H1-receptor antagonists do not inhibit stimulation of acid production in the secretory canaliculi. They may, however, interfere with a mechanism preventing acid from leaving the parietal cell. Such a mechanism may contribute to the delay in appearance of acid in the gastric lumen after stimulation of gastric acid production.

Effect of nicotine on the enterochromaffin like cells of the oxyntic mucosa of the rat

Smoking has an unfavourable effect on peptic ulcer disease. The pathophysiological mechanisms underlying this effect are not known. The enterochromaffin like (ECL) cell is the cellular source of histamine participating in the regulation of acid secretion. The ECL cell is under functional and trophic control of gastrin and the vagus nerves. Nicotine may affect acid secretion through vagal pathways. Furthermore, nicotine may also stimulate neuroendocrine cells. The present study examined if chronic nicotine administration could stimulate the function and growth of the ECL cell. Rats inhaled nicotine vapour at a concentration of approximately 6.2 mumol/m3, 20 hours/day, 5 days/week for 11 weeks. Steady state plasma nicotine concentration was 461.8 (137.5 (SD)) nmol/l. The ECL cell density, histamine content and histidine decarboxylase activity of the oxynitic mucosa were similar to the controls. We also examined the effect of acute nicotine stimulation on the acid output and histamine release from the totally isolated vascularly perfused rat stomach. Nicotine did not stimulate acid secretion or histamine release. Thus no evidence could be provided to support the hypothesis that nicotine exerts its negative effects on peptic ulcer disease by stimulating the ECL cell.

The enterochromaffin-like (ECL) cell. Physiological and pathophysiological role

Histamine has a central role in the regulation of gastric acid secretion. This histamine is produced by and released from the enterochromaffin-like (ECL) cell which accordingly has a key-regulatory role in the oxyntic mucosa. Gastrin and the vagal nerves stimulate the formation and release of histamine from the ECL cell. Moreover, gastrin and the vagal nerves also stimulate the proliferation of the ECL cell. An increased ECL cell density may partly explain the increased acid secretion in patients with duodenal ulcer, particularly in patients with Zollinger-Ellison syndrome. The reduced potency of histamine-2 blockers in patients with Zollinger-Ellison syndrome is probably due to increased histamine release by an elevated ECL cell mass. Prolonged and profound hypergastrinemia may lead to ECLomas. Moreover, a proportion of diffuse gastric carcinomas may originate from ECL cells.

Enterochromaffin-like cells in rat stomach respond to short-term infusion of high doses of cholecystokinin but not to long-term, sustained, moderate hyperCCKemia caused by continuous cholecystokinin infusion or pancreaticobiliary diversion

The histamine-producing enterochromaffin-like (ECL) cells in the oxyntic mucosa are controlled by gastrin. An acute gastrin challenge induces release and accelerated resynthesis of ECL cell histamine. Long-term stimulation with gastrin causes ECL cell hyperplasia. We set out to study whether the ECL cells respond not only to gastrin but also to cholecystokinin (CCK). A wide dose range of gastrin-14 sulfated and -17 non-sulfated and CCK-8 sulfated (CCK-8s) and non-sulfated (CCK-8) was infused intravenously to rats for 3 h. The activity of the histamine-forming enzyme was measured at termination of infusion. Gastrins and CCK-8s were equally effective in activating the enzyme, whereas sulfated CCK-8 was notably less potent than the other three peptides. Clearly, the receptor responsible for activation of the ECL cells distinguishes poorly between gastrin-17 and CCK-8s, which is in line with the characteristics of the CCK-B receptor. Moreover, neither the response to gastrin-17 nor that to CCK-8s was affected by concomitant infusion of devazepide (200 micrograms/kg/h), a selective CCK-A-receptor antagonist. One group of rats received CCK-8s continuously via a minipump. Another group of rats was subjected to pancreaticobiliary diversion (PBD), which increases the plasma CCK concentration 10- to 20-fold. The rats were killed 7 or 10 weeks later, respectively, and the stomachs were analyzed with regard to mucosal growth and ECL cell hyperplasia. HyperCCKemic rats had increased pancreatic weights but showed no signs of growth stimulation in the stomach and no ECL cell hyperplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Biologic and immunologic gastrin activity in serum of patients with gastrinoma. Bioassay of gastrin activity in serum

The biologic gastrin activity in serum from 14 patients with the Zollinger-Ellison syndrome was assessed by the stimulation of histamine release and acid secretion from the isolated vascularly perfused rat stomach and compared with the immunologic activity as determined by radioimmunoassay using an antibody directed towards the active site of the gastrin molecule. Biologic gastrin activity assessed by the stimulation of histamine release was more closely correlated to immunologic gastrin activity than biologic activity assessed by the stimulation of gastrin acid secretion. This study does not contradict the concept that gastrin stimulates acid secretion at least partly by releasing histamine and also shows that the immunologic gastrin activity determined with the help of an antibody directed towards the active site reflects biologic activity.

Trophic effect of gastrin on the enterochromaffin like cells of the rat stomach: establishment of a dose response relationship

Gastrin was given to rats by continuous subcutaneous infusion through implanted osmotic minipumps in doses covering a wide range of the dose response relationship for gastrin with regard to the trophic effect on the enterochromaffin like cells of the oxyntic mucosa. Thirty five rats were divided into five groups (each of seven rats), one group receiving a control solution of 1% albumin, the others receiving gastrin in 1% albumin at doses of 2.5, 5, 10, and 15 micrograms/kg/h, respectively. The plasma gastrin concentrations in the various groups increased in the same order of magnitude as expected from the gastrin doses given. Gastrin induced a dose dependent increase in enterochromaffin like cell density, oxyntic mucosal histamine concentration and histidine decarboxylase activity up to the dose of 5 micrograms/kg/h, where the increase levelled off. Hence, the dose response relationship for the trophic effect of gastrin on the enterochromaffin like cells seems to follow a polynomial rather than a linear function. These findings may also contribute to the understanding of the trophic effect of gastrin on enterochromaffin like cells in man with conditions associated with hypergastrinaemia.

Hyperplasia of histamine-depleted enterochromaffinlike cells in rat stomach using omeprazole and alpha-fluoromethylhistidine

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.

Effects on the rat oxyntic mucosa of the histamine2-antagonist loxtidine and the H+, K(+)-ATPase inhibitor omeprazole

The present study examined whether histamine could affect the growth of the enterochromaffin-like (ECL) cell and the parietal cell. The effects of the unsurmountable histamine H2-receptor antagonist loxtidine (80 mg/kg) and the H+, K(+)-ATPase inhibitor omeprazole (100 mumol/kg) were compared in female Sprague-Dawley rats. Both drugs were given by gavage once daily for 3 months. Omeprazole induced a more pronounced and sustained hypergastrinaemia than loxtidine. In spite of marked hypergastrinaemia during most of the day, even in the loxtidine-treated rats, the weights of the stomach and oxyntic mucosa were elevated only in the omeprazole-treated rats. The ECL cell density was slightly higher in the loxtidine- than in the omeprazole-treated rats. Both treatments elevated the gastrin-stimulated histamine release from the vascularly perfused stomach. The parietal cell density was unaffected by omeprazole treatment, whereas it tended to be reduced in the loxtidine-treated rats. Simultaneous administration of loxtidine and omeprazole reduced the sustained hypergastrinaemia induced by omeprazole given alone. The present study may indicate that histamine inhibits the growth of the ECL cell, but further studies are needed to elucidate if histamine has any trophic effect on the parietal cells.

Reversibility of the cell kinetic changes induced by omeprazole in the rat oxyntic mucosa. An autoradiographic study using tritiated thymidine

Both oxyntic mucosal progenitor cells and enterochromaffin-like (ECL) cells are under the trophic control of gastrin. We studied the effect of discontinuing omeprazole-induced hypergastrinemia on cell proliferation and ECL cell function in the rat oxyntic mucosa. All rats had hypergastrinemia after 16 days' omeprazole administration, and the proliferation rate of both progenitor and ECL cells was increased, whereas it was decreased 5 days after withdrawal of omeprazole. Circulating gastrin had normalized by then. The proliferative activity of the progenitor cells returned to normal within 10 days, whereas that of the ECL cells remained suppressed for at least 20 days. The histidine decarboxylase activity of the ECL cells changed in parallel with their proliferative activity. These data suggest either a down-regulation of membrane receptors or the involvement of still unknown inhibitors of mitotic activity and ECL cell function in the oxyntic mucosa.

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.

Histidine decarboxylase gene expression in rat fundus is regulated by gastrin

The conversion of histidine to histamine by histidine decarboxylase (HDC) is of central importance in the control of vertebrate acid secretion. We have used PCR-generated probes to study the regulation of HDC gene expression in rat fundic mucosa. When circulating gastrin levels were lowered by fasting or elevated by treatment with omeprazole, there were parallel changes in HDC mRNA abundance. However, when animals with elevated gastrin levels were concurrently treated with the gastrin/CCK-B receptor antagonist PD 134308, HDC mRNA levels were not increased. These data are consistent with the hypothesis that HDC gene expression is regulated by gastrin, over the physiological range of circulating hormone concentrations.

Radioimmunoassay of histamine

Histamine is formed by decarboxylation of the amino acid histidine and is found both in plants and in animals, including man. In man it has important biologic functions. To assess the physiologic role of histamine, however, it is necessary to have a reliable and convenient method to determine its concentration in biologic fluids and tissue. Histamine has been determined by bioassay, chemically by different modification of a fluorometric method, by radioenzymatic methods, and, recently, by immunoassays. Immunoassay of histamine has, however, been difficult to establish, mainly as a result of problems with the production of an antibody with histamine specificity. This is due to the general occurrence of histamine in all animal species. By binding histamine to different ligands, several researchers have succeeded in producing antibodies against antigens in which histamine is integrated. Treating samples and histamine standard with the same coupling agent, reliable and specific radioimmunoassays of histamine have been established. We have for some years utilized a commercial radioimmunoassay of histamine and confirmed its convenience, specificity, and sensitivity. In some patients taking a histamine-2 blocker (cimetidine or ranitidine) we have detected an increase in plasma histamine which also tended to be increased after proximal gastric vagotomy and in patients with gastric ulcer compared with patients with duodenal ulcer. In rats treated with high doses of omeprazole for 90 days we found an increase in the enterochromaffin-like cell mass and in histamine concentration in the oxyntic mucosa which was reflected by an increase in plasma histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspects of the regulation of gastric histamine release

Histamine is found in large amounts in the gastric mucosa and plays an essential role in the regulation of acid secretion. It is thought to stimulate acid secretion directly after being released by the other two major secretagogues (gastrin and acetylcholine) (the mediator hypothesis) or to potentiate the action of the other two secretagogues (the interaction hypothesis). Recent studies with isolated, vascularly perfused rat stomach have shown that gastrin in physiologic concentrations elicits a release of histamine sufficient to explain its acid-stimulatory effect. Vagal nerve stimulation, on the other hand, only gives a faint histamine release, indicating that the vagal acid stimulation is mainly mediated by a direct stimulation of the parietal cell. Furthermore, the gastrin-stimulated histamine release seems to be mediated by a calcium-dependent mechanism. Somatostatin inhibits gastrin-stimulated histamine release via a paracrine mechanism, and a prostaglandin E1 analogue (misoprostol) has been shown to be a potent inhibitor of base-line and gastrin-stimulated histamine release. These studies show that the modulation of histamine release may be a central regulatory mechanism of gastric acid secretion. Although these studies have been done in rats, there are indications that these results are of a general nature nd valid for other species as well.

Enterochromaffin-like tumour cells in the diffuse but not the intestinal type of gastric carcinomas

Gastrin may play a role in gastric carcinogenesis, as indicated by an increased frequency of gastric carcinomas in patients with pernicious anaemia and the fact some human gastric cancer cell lines carry the gastrin receptor. Recently, it has been shown that the acid-stimulatory effect of gastrin may be solely mediated by histamine release from the enterochromaffin-like (ECL) cell, on which gastrin has a specific trophic effect. We therefore found it of interest to examine human gastric carcinomas for the presence of ECL tumour cells by using silver staining and chromogranin immunohistochemistry. We found evidence of ECL cell-derived tumour cells in 40% of the diffuse gastric carcinomas but no such tumour cells in the intestinal type of gastric carcinoma. This may suggest that diffuse gastric carcinomas, like malignant gastric tumours of the mastomys, are in fact malignant ECLomas.

Pentagastrin-stimulated histamine release and acid secretion from the totally isolated vascularly perfused rat stomach

This study was performed to examine the effect of cAMP levels on histamine release in the isolated rat stomach. Pentagastrin-induced histamine release was unaffected by phosphodiesterase inhibition, and pentagastrin itself had no phosphodiesterase-like effect. The results support previous observations showing that histamine is likely to be the mediator of the acid secretagogue effect of (penta) gastrin.

Effect of the histamine-1 antagonist astemizole alone or with omeprazole on rat gastric mucosa

The stimulation of acid secretion by gastrin may in the rat be explained solely by gastrin-induced histamine release. This study was done to examine whether histamine could mediate the general trophic effect of gastrin on the oxyntic mucosa, by using a long-acting selective histamine-1 antagonist (astemizole) alone or with omeprazole-induced hypergastrinaemia for 90 days in female Sprague-Dawley rats. At day 90, isolated vascularly perfused rat stomachs were prepared to study maximal gastrin- and histamine-stimulated acid and pepsinogen outputs and maximal gastrin-stimulated histamine release. Oxyntic mucosa morphometry, mucosal histamine and pepsinogen contents, and plasma gastrin and histamine levels were also determined. For the first time, omeprazole has been found to inhibit gastric emptying and to increase plasma histamine. As compared with controls, astemizole alone did not influence plasma gastrin, increased plasma histamine in only some rats, and gave a slight increase in all other variables. Together with omeprazole, it further increased variables already stimulated by omeprazole. Thus, mucosal thickness, histamine concentration, and chief-cell density in oxyntic mucosa were significantly higher in astemizole/omeprazole-treated rats than in omeprazole-treated rats. Gastrin-stimulated histamine release was increased in both astemizole- and omeprazole-treated rats. For all rats plasma histamine was significantly correlated with plasma gastrin and with numerical fundic argyrophil cell density. In conclusion, the present study confirms the trophic effect of gastrin and shows a slight trophic effect of astemizole on the oxyntic mucosa. It also shows that plasma histamine may reflect the argyrophil cell density in the oxyntic mucosa and that omeprazole inhibits gastric emptying.

Pentagastrin and histamine in the regulation of gastric mucosal blood flow

The current state of our knowledge concerning mediator(s) of the increase in gastric mucosal blood flow that occurs during pentagastrin- and histamine-stimulated acid secretion is reviewed. Evidence for a role for adenosine, prostaglandin, and histamine is presented and discussed. The dose relationship between the acid-stimulatory and the vascular permeability effects of histamine is also presented.

Histamine and the stomach: introduction

The physiologic role of histamine in the stomach has for many years been a subject of controversy. The introduction of histamine-2-receptor antagonists and, later, of proton pump inhibitors has not only stimulated the interest in the topic but has also made it relevant for the clinician. The main and still unsettled issue is the interrelationship between histamine and gastrin on the parietal cell.

Trophic effect of histamine on the stomach

On the basis of clinical observations and experimental animal studies it has been established that gastrin has a trophic effect on the oxyntic mucosa. On the other hand, histamine, being at least as efficient as gastrin as an acid secretagogue, has experimentally been reported not to have such trophic effect. However, during the last few years both endogenously and exogenously induced hypergastremia have been shown to have a specific trophic effect on the enterochromaffin-like (ECL) cell and a less pronounced and later detectable general trophic effect on the oxyntic mucosa. Moreover, in the rat (the species in which most of the trophic studies have been done) the acid-stimulatory effect of gastrin may be solely explained by stimulation of histamine release from ECL cells. Therefore, it seemed natural to evaluate whether the general trophic effect of gastrin could also be caused by histamine or another substance released from the ECL cells. In this review we challenge the concept that maximal pentagastrin-stimulated acid secretion only reflects the parietal cell mass, since the acid-stimulatory effect of gastrin is mediated by histamine release. Therefore, maximal pentagastrin-stimulated acid secretion reflects both the ECL cell mass and the parietal cell mass. With regard to the possible trophic effect of histamine, we show that the doses previously used have been inadequate. Furthermore, histamine has been reported to have a trophic effect on the parietal cell in the dog; some patients with hyperhistaminemia have an increased maximal histamine-stimulated acid secretion, suggesting an increase in the parietal cell mass; and there is parietal cell hyperplasia in the oxyntic mucosa surrounding the histamine-producing carcinoids in mastomys.(ABSTRACT TRUNCATED AT 250 WORDS)

The gastrin receptor assay

Gastrin is a major physiologic regulator of gastric acid secretion and growth of the oxyntic mucosa. Biologically active radiolabelled hormones may be used to characterize and localize receptors for peptide hormones. The cellular localization of the gastrin receptor in the fundic mucosa, however, is still a matter of great debate owing to difficulties in developing a gastrin receptor binding assay. Despite considerable work in several laboratories, the criteria for true receptor binding have not yet been fulfilled. The preparation of a suitable tissue receptor material (plasma membranes or isolated cells) from the heterocellular fundic mucosa seems to be the major problem. This problem may be related to the fact that the receptors are only present on the enterochromaffin-like cells (ECL), which constitute but a minor fraction of the cells in the oxyntic mucosa. Furthermore, the second messenger of gastrin is still not known, and the poor functional responsiveness of isolated cells and the oxyntic glands to gastrin further complicates the evaluation of the gastrin receptor. In this review the different steps in the gastrin receptor assay (the labelling of gastrin, preparation of the receptor, and the incubation and correlation of the binding and biologic effect of gastrin) are discussed.

Gastric somatostatin: a paracrine regulator of acid secretion

The presence of acid in the lumen of the gastric fundus induces release of somatostatin close to the parietal cells; this acts to attenuate acid secretion in response to secretagogues, such as histamine and gastrin. The release of somatostatin within the stomach is further regulated by the activity of cholinergic neurons that inhibit somatostatin release and thus augment acid secretion (disinhibition), and noncholinergic (bombesin) neurons that stimulate somatostatin release and thus attenuate acid secretion. The influence of these neurons and the participation of somatostatin as a paracrine regulator of acid secretion has been probed and validated by the use of selective antagonists (atropine and a bombesin antagonist), somatostatin antiserum and pertussis toxin. Similar mechanisms exist in the distal antral segment of the stomach for the paracrine regulation of gastrin release by somatostatin.

Effects of cholecystokinin and cholinergic receptor blockade on guinea pig pepsinogen secretion

Although cholecystokinin (CCK) has been reported to stimulate pepsinogen secretion, this action has been poorly characterized. To assess the ability of CCK to regulate mammalian pepsinogen secretion, guinea pig fundic mucosa was incubated in Ussing chambers with CCK-8, carbamylcholine, and pentagastrin, and with cholinergic and CCK antagonists. CCK-8 stimulated pepsinogen secretion at 10(-10) M, with an ED50 of 10(-9) M and maximally (26-fold over basal) at 10(-8) M. Carbachol stimulated pepsinogen and acid secretion with an ED50 of 3 x 10(-7) M and maximally at 10(-6) M. Pentagastrin (10(-9) M-10(-6) M) did not affect acid or pepsinogen secretion, whereas gastrin-I (10(-6) M) stimulated acid secretion slightly but did not alter pepsinogen secretion. L364, 718 (10(-5) M), a specific CCK peripheral receptor antagonist, abolished all pepsigogic effects of 3 x 10(-9) M CCK-8 without altering basal acid or pepsinogen secretion or mucosal electric characteristics. L364,718-treated tissues unresponsive to CCK-8 nevertheless secreted pepsinogen and acid in response to 3 x 10(-7) M carbachol identically to control carbachol-treated preparations. Atropine (10(-5) M) blocked the response to 3 x 10(-7) M carbachol without inhibiting 10(-9) M CCK stimulation. These results support a specific receptor-mediated role for cholecystokinin in the physiologic regulation of guinea pig pepsinogen secretion.

Visualisation of the gastrin receptor within rat mucosa using a biotinylated gastrin antagonist

We have previously demonstrated that the peptide Boc-L-Trp-L-Leu-beta-Ala is a potent and specific antagonist of pentagastrin-stimulated acid secretion in both the rat and the dog. Using conventional solution phase methodology, the analogue biotinyl-L-Trp-L-Leu-beta-Ala was prepared in reasonable yield and purity and applied to cryostat sections of rat intestinal and other tissues. The sections were exposed to 5-10 micrograms of peptide and the bound analogue was visualised using streptavidin-fluorescein. The binding of the analogue was demonstrated in sections from fundus, duodenum, ileum, colon, and lung. However, the analogue failed to bind to tissue from the pancreas, heart, kidney, or liver. The binding of the probe was greatly reduced or completely inhibited by preincubation with Boc-L-Trp-L-Leu-beta-Ala, pentagastrin, or gastrin 1-17. The distribution of the cells recognised by the probe was consistent with the distribution of histamine-containing enterochromaffin-like cells. The results of this study may have some bearing on current theories of the mechanism of gastrin-stimulated acid release.

Rat gastric histamine release: a sensitive gastrin bioassay

Acid secretion and histamine release from the totally isolated vascularly perfused rat stomach are sensitive parameters for the biological effects of gastrin. By optimalizing the Ca2+ concentration of the vascular perfusate the sensitivity for stimulation of acid secretion was improved from 65 to 16 pmol/l gastrin 1-17 (G-17). Measurement of venous histamine before and after gastrin in each stomach preparation excluded inter-stomach variability and improved the sensitivity to 2 pmol/l G-17. This is the most sensitive gastrin bioassay reported, with a detection limit comparable to that of radioimmunoassay.

Histamine release in the isolated vascularly perfused stomach of the rat: regulation by autoreceptors

1. In the isolated vascularly-perfused stomach of the rat, gastrin 1-17 (520 pmol 1(-1)) increased acid output from basal values of 13.7 +/- 2.7 to 92.5 +/- 11.4 mumol h-1 and venous histamine output from 10.1 +/- 2.3 to 54.7 +/- 7.9 nmol h-1 (mean +/- s.e.mean). 2. The H1 receptor agonist 2-methylhistamine (10 mumol 1(-1)) increased acid output to 21.6 +/- 2.9 mumol h-1 (P less than 0.05) and reduced basal histamine output to 4.0 +/- 0.8 nmol h-1 (P less than 0.05). Gastrin-stimulated acid secretion and vascular histamine output was not significantly affected by 2-methylhistamine (10 mumol 1(-1)). 3. The H2 receptor agonist, impromidine, dose-dependently increased basal acid secretion, reaching a maximal value of 145.5 +/- 11.7 mumol h-1 with impromidine (10 mumol 1(-1)), and maximal gastrin-stimulated acid secretion to 167.4 +/- 15.1 mumol h-1 with impromidine (10 mumol 1(-1)). Impromidine dose-dependently inhibited basal and gastrin-stimulated vascular histamine output. 4. The H3 receptor agonist R-a-methylhistamine, (1 and 10 mumol 1(-1)) minimally increased basal acid secretion. R-a-methylhistamine (10 mumol 1(-1)) did not significantly affect maximal gastrin-stimulated acid secretion. Basal and gastrin-stimulated vascular histamine outputs decreased to 4.0 +/- 0.8 (P less than 0.05) and 24.7 +/- 4.7 nmol h-1 (P = 0.05) with R-a-methylhistamine (10 mumol 1(-1)). 5. The H2 receptor antagonist ranitidine (2 mumol 1(-1)) did not inhibit basal acid secretion, but acid outputs with gastrin and all histamine agonists were reduced. Ranitidine did not affect histamine release in the basal state, with gastrin or with any histamine agonist tested. 6 We conclude that gastric histamine release in the rat is regulated via a histamine H2 receptor sensitive to the histamine agonists tested, but not to ranitidine. It is unlikely that the inhibition of histamine release is secondary to increased gastric acidity.

The effect of gastrin-releasing peptide on acid secretion and the release of gastrin, somatostatin, and histamine in the totally isolated, vascularly perfused rat stomach

We have studied the effect of gastrin-releasing peptide (GRP) on exocrine and endocrine secretion in the totally isolated, vascularly perfused rat stomach with or without concomitant infusion of a potent somatostatin antiserum. GRP (1 nM) showed a marginal acid-stimulatory effect (base line, 11.6 +/- 2.3 mumol/60 min, and after GRP, 20.0 +/- 2.2 mumol/60 min; p = 0.05). GRP significantly increased gastrin and somatostatin release to the venous effluent, and the venous gastrin concentration increased significantly during concomitant infusion of somatostatin antiserum. Furthermore, GRP inhibited histamine liberation, and somatostatin antiserum reversed this effect. The antiserum did not significantly stimulate acid secretion. Thus, the present study shows that GRP directly or indirectly affects both acid secretion and the release of gastrin, somatostatin, and histamine in the rat stomach.

Muscarinic M2 stimulation releases histamine in the totally isolated, vascularly perfused rat stomach

The present study examines the role of histamine in the stimulation of acid secretion induced by vagal nerve stimulation and by the muscarinic M1 agonist McN-A-343 in the totally isolated, vascularly perfused rat stomach. The stimuli were combined with an agent stimulating the cAMP system (isobutyl methylxanthine (IMX) or forskolin), a muscarinic antagonist (atropine or pirenzepine), or a histamine H2 antagonist (ranitidine). IMX and forskolin potentiated McN-A-343-stimulated acid secretion, yielding acid outputs of 280% and 260% of the sum of McN-A-343- and IMX-, or McN-A-343- and forskolin-stimulated outputs, respectively. Ranitidine inhibited acid secretion stimulated by McN-A-343 alone or in combination with IMX, whereas the forskolin-stimulated secretion was not influenced by the H2 antagonist. This strongly indicates that endogenous histamine potentiates muscarinic M1-stimulated acid secretion by increasing parietal cell cAMP. Vagal nerve stimulation with IMX increased acid output from 12.2 +/- 3.0 to 49.2 +/- 9.3 mumol/60 min (mean +/- SEM). The M1 antagonist pirenzepine and the M1/M2 antagonist atropine both significantly (p less than 0.01) inhibited vagally stimulated acid secretion. Histamine output as measured in the venous effluent was unchanged by McN-A-343, whereas nerve stimulation induced a clear increase in venous histamine output, from 101 +/- 21 before to 212 +/- 28 pmol/min (mean +/- SEM) after initiation of nerve stimulation. Histamine release was reduced to base-line levels by atropine but only insignificantly inhibited by pirenzepine, indicating a muscarinic M2 stimulation of histamine release in the rat stomach.

Ionized calcium influences gastrin stimulated histamine release and acid secretion, but not histamine stimulated acid output in the totally isolated vascularly perfused rat stomach

When changing from bovine serum albumin to dextran T70 as colloid without adjusting the total calcium concentration in the vascular perfusate of the totally isolated vascularly perfused rat stomach, we noticed a drastic fall in gastrin-stimulated acid secretion. In the present study the effect of the two colloids on ionized calcium in the vascular perfusate as well as the effect on acid secretion and vascular histamine release were studied. There was no difference in gastrin-stimulated acid secretion or vascular histamine release between the two colloids after adjusting the total calcium concentrations so that ionized calcium was similar. Whereas baseline acid secretion showed no marked dependency of ionized calcium within the range tested (0.73-1.54 mmol l-1, gastrin-stimulated acid secretion was highly dependent on ionized calcium being reduced at the higher concentration of Ca2+. Histamine stimulated acid secretion, on the other hand, was virtually unaffected by the concentration of ionized calcium in the same range. Like gastrin-stimulated acid secretion, gastrin-stimulated histamine release was inhibited at higher Ca2+ concentrations. Thus, elevated Ca2+ concentrations seemed to reduce gastrin-stimulated acid secretion by inhibiting vascular histamine release.

The effect of misoprostol on base-line and stimulated acid secretion and on gastrin and histamine release in the totally isolated, vascularly perfused rat stomach

The effects of the prostaglandin E1 analogue misoprostol on base-line and stimulated (gastrin, histamine, and the muscarinic M1 agonist McN-A-343) acid secretion, base-line and gastrin-stimulated histamine release, and base-line and McN-A-343-stimulated gastrin release in the totally isolated, vascularly perfused rat stomach were studied. At a concentration of 1 nM, misoprostol significantly (p less than 0.01) inhibited base-line acid secretion from 13.7 +/- 2.7 to 4.8 +/- 0.7 mumol/60 min, histamine-stimulated acid secretion from 99.9 +/- 15.1 to 21.8 +/- 8.2 mumol/60 min, maximal gastrin-stimulated secretion from 92.5 +/- 11.4 to 3.1 +/- 0.6 mumol/60 min, and maximal McN-A-343-stimulated secretion from 60.0 +/- 8.9 to 6.8 +/- 2.6 mumol/60 min (mean +/- SEM). Likewise, misoprostol significantly inhibited base-line vascular histamine release (p less than 0.05) from 10.1 +/- 2.3 to 3.7 +/- 0.7 nmol/60 min and gastrin-stimulated release (p less than 0.01) from 54.7 +/- 7.9 to 20.2 +/- 4.1 nmol/60 min (mean +/- SEM). The gastrin release was not affected by misoprostol. We conclude that misoprostol inhibits acid secretion both by a direct effect on the parietal cell and by inhibiting endogenous histamine release.

The effect of somatostatin on baseline and stimulated acid secretion and vascular histamine release from the totally isolated vascularly perfused rat stomach

The effect of somatostatin-(1-14) (S1-14) on the gastrin- and histamine-induced acid secretion and gastrin-evoked vascular histamine release was studied in isolated vascularly perfused rat stomachs being continuously perfused by a gassed buffer containing 10% ovine erythrocytes and 50 microM isobutyl methylxanthine (IMX). Concentrations of gastrin (520 pM) and histamine, (0.5 microM) were chosen to give acid secretion in the same range (61.5 +/- 7.0 and 49.4 +/- 9.4 mumol/60 min). S1-14 induced a concentration-dependent decrease in acid secretion stimulated by both gastrin and histamine. Even at the lowest concentration examined (0.1 nM) somatostatin gave a significant inhibition of both gastrin- and histamine-stimulated acid secretion. The inhibitory effect was, however, most marked for gastrin-stimulated acid secretion (P less than 0.05 at 1 nM concentration of S1-14). Gastrin gave an immediate and marked vascular histamine release which was inhibited by somatostatin in the higher concentrations (1.0 and 5.0 nM). Somatostatin at the lowest concentration tested (0.1 nM) did not inhibit the gastrin-induced vascular histamine release although it did inhibit acid secretion. Furthermore, baseline histamine release was not affected by somatostatin. This study suggests that somatostatin inhibits acid secretion both via a direct effect of the parietal cell and by inhibiting gastrin-induced histamine release. Baseline histamine release is regulated by a mechanism not sensitive to somatostatin.