Gastrin Release from Antral G Cells Stimulated with Secretin

Recently, gastrinoma cells were demonstrated to release gastrin when directly stimulated by secretin both in vivo and in vitro. In this study, the reaction of antral G cells was investigated. Secretin was injected into the right gastroepiploic artery in canines, and into the common hepatic artery during a selective arteriography in patients without gastrinomas. G cells obtained from the antrum of rats were attached to 0.45-microns filters and irrigated with medium containing secretin. The serum gastrin concentration increased rapidly in significant amounts and very quickly after an intraarterial injection of secretin, both in humans and in dogs. The rate of gastrin release from the rat antral G cells in vitro increased significantly when the medium contained secretin. In conclusion, secretin stimulated gastrin release from antral G cells both in vivo and in vitro.     

Gastrin secretion from human antral G cells in culture

Receptor-dependent and -independent regulation of gastrin secretion from cultured human antral G cells was investigated. Human antral mucosal cell preparations that were enriched for G cells were obtained by sequential incubations with collagenase and ethylenediaminetetraacetic acid, centrifugal elutriation, and short-term culture. After a 2-day incubation period, gastrin- and somatostatin-containing cells accounted for 15% and 5%, respectively, of the total adhered-cell population. Forskolin, A23187, and beta-phorbol 12 myristate 13-acetate stimulated basal gastrin secretion from cultured human G cells in a concentration-dependent fashion. These results indicate that gastrin release could be mediated by elevations in cytosolic cyclic adenosine monophosphate levels, calcium influx, or activation of protein kinase C. A direct stimulatory role for bombesin- and gastrin-releasing peptide was supported by experiments showing concentration-dependent enhancement of gastrin release by bombesin from 0.01 fmol/L to 10 nmol/L. The putative bombesin antagonist [Leu13-psi-CH2NH-Leu14] bombesin augmented basal gastrin levels by itself and produced weak inhibition of bombesin-induced gastrin secretion from human antral G cells. Somatostatin potently suppressed forskolin- and bombesin-mediated gastrin release but did not significantly alter basal gastrin levels. These results suggest that bombesin and somatostatin directly activate and inhibit G-cell function via specific and sensitive receptors. Furthermore, the adenylate cyclase and phosphatidyl inositide second messenger systems seem to be intracellular mediators of gastrin secretion from human antral G cells.     

Endogenous Gastrin Release and Antral Gastrin Concentration in Gastroesophageal Reflux Patients and Normal Subjects

In this study we compared both endogenous gastrin release to a known gastrin stimulant, phenylalanine, and fasting antral mucosal gastrin concentration in normal subjects and patients with documented gastroesophageal reflux. Resting lower esophageal sphincter pressure in the reflux patients (14.7 ± 1.5 mm Hg) was significantly less ( p < 0.01) than in the normal subjects (27.5 ± 2.7 mm Hg). Basal serum gastrin concentrations were similar in the two groups. There were significant ( p < 0.05) increases in peak serum gastrin in response to intragastric administration of phenylalanine in both normal subjects (20.6 ± 6.7 pg/ml, p < 0.05) and refluxers (22.4 ± 3.0 pg/ml, p < 0.01) but there were no significant differences in these responses between normals and refluxers. Mean integrated gastrin response to phenylalanine in the reflux patients (812 ± 116 PG ml⁻¹ h⁻¹) was slightly higher than that in normals (609 ± 328 pg ml⁻¹ h⁻¹) although the difference was not significant. Antral gastrin concentration was slightly higher in reflux patients (15.7 ± 2.2 ng/mg tissue) than in normals (10.4 ± 4.2 ng/mg tissue), although this difference was not significant. There was no correlation between antral gastrin concentration and either integrated serum gastrin response or gastric acid output. We conclude that there is no difference between patients with gastroesophageal reflux and normal subjects with regard to serum gastrin levels, endogenous gastrin release, or antral gastrin concentration. These observations suggest no role for gastrin in the mediation of lower esophageal sphincter incompetence or the pathophysiology of gastroesophageal reflux.     

Regulation of rat antral gastrin and somatostatin gene expression during starvation and after refeeding.

Antral gastrin and somatostatin gene expression during starvation and after refeeding with liquid meals of varying composition were studied. Northern and slot-blot hybridization analyses showed that starvation caused a marked decrease in antral gastrin messenger RNA (mRNA) level by 12 hours associated with an increase in somatostatin mRNA. After 48 hours of fasting, antral gastrin mRNA was 26% and somatostatin mRNA was 136% of their prefasting levels. Refeeding caused increased 2-hour integrated gastrin mRNA levels after liquid peptone (+45%), phenylalanine (+31%), and olive oil (+13%), but no changes were observed with glucose or saline solutions. Integrated 2-hour immunoreactive antral gastrin content was increased after peptone (+106%), phenylalanine (+68%), and olive oil (+32%) meals but was not increased after glucose (-11%) or saline (-10%). In some cases, both gastrin mRNA and peptide responses could be measured as early as 15 minutes. The same nutrients that increased gastrin mRNA levels caused decreased 2-hour integrated somatostatin mRNA levels; peptone (-30%), phenylalanine (-28%), and olive oil (-21%), but neither glucose nor saline, altered somatostatin mRNA levels. These results suggest that antral gastrin and somatostatin genes were regulated in opposite directions, in a coordinate manner, by specific gastric nutrients that stimulate gastrin release.     

Two types of Zollinger-Ellison syndrome: immunofluorescent, cytochemical and ultrastructural studies of the antral and pancreatic gastrin cells in different clinical states

In this survey the antral, pancreatic and, where present, the neoplastic gastrin cells, were studied in eight cases of the Zollinger-Ellison syndrome. The antral G cells alone were studied in one case of Z-E syndrome, seven cases of simple duodenal ulcer, and five cases of pernicious anaemia.The Z-E cases were divided into two numerically equal groups. The first group had ;short' histories, high serum gastrin levels, and profound antral G cell hyperplasia. The second group had ;long' histories, relatively lower serum gastrin levels, normal antral G cells, and either pancreatic D cell hyperplasia or gastrinoma.Antral G cell hyperplasia, with maximal gastrin storage and normal serum gastrin levels, was found in the duodenal ulcer cases. Antral G cell hyperplasia with minimal storage and high serum gastrin levels was observed in the cases of pernicious anaemia.On the basis of our findings we propose that there exist at least two distinct types (or perhaps stages) of the Z-E syndrome. Suggestions for their pathogenesis are offered.     

The effect on gastrin secretion of agents which increase the intracellular concentration of 3',5'-adenosine monophosphate.

An in vitro technique that allows study of gastrin secretion from isolated pieces of rat gastric antrum was used to study the effect on gastrin release of agents known to increase intracellular cAMP levels. Isuprel (10(-5)M), PGE1 (10(-5)M), theophylline (10(-4)M), and dibutyryl cAMP (5 X 10(-4)M) did not affect gastrin release when used alone, but each enhanced arginine-stimulated gastrin release. A biphasic pattern of gastrin release in response to arginine was seen in all experiments. The studies emphasize the close functional similarity between the antral G cells and the B cells of the pancreatic islet.     

Effect of Platelet-Activating Factor on Gastrin Release from Cultured Rabbit G-Cells

Gastric infection with Helicobacter pylori is associated with hypergastrinemia. Platelet activating factor (PAF) is produced in H. pylori-infected mucosa. The effects of PAF on gastrin release from cultured antral rabbit G cells were examined. Rabbit antral G-cells were obtained by collagenase-EDTA digestion and enriched by centrifugal elutriation. After 40 hr in culture, gastrin release in response to PAF was assessed. PAF stimulated gastrin release in a dose-dependent manner. A maximal release of 67% above basal was seen with PAF at 100 nM. PAF also enhanced the gastrin release stimulated by forskolin and bombesin. PAF-stimulated gastrin release was abolished by a PAF-receptor antagonist. Gastrin release stimulated by PAF was abolished by chelation of intra- or extracellular calcium or the L-type calcium channel inhibitor verapamil as well as by the protein kinase C inhibitor chelerythrine. Platelet-activating factor may contribute to the hypergastrinemia of H. pylori infection by stimulating gastrin release from G cells. PAF-stimulated gastrin release involves influx of extracellular calcium via L-type channels and activation of protein kinase C.     

Gastrin and the ultrastructure of G cells in the fasting rat.

The effect of fasting on serum and antral gastrin concentrations and G cell ultrastructure in the rat has been examined using a radioimmunoassay and quantitative electron microscopy. Serum gastrin levels in fasting animals were markedly reduced and there was also a significant decrease in antral gastrin concentrations after 48 hours and 72 hours of fasting. This was associated with a significant fall in the granule content and cytloplasmic volume of individual G cells, at its greatest by 48 hours. A relative absence of electron dense granules in the Golgi zones of cells from animals fasted for 72 hours suggested a paucity of newly formed granules, but fasting produced no detectable change in the electron density of the granule population taken as a whole. The results indicate that, during fasting, release and then synthesis of gastrin is inhibited, so that granule stores and cell size diminish. The correlation between the granule content of G cells and the antral content of gastrin suggests that hormone release occurs by exocytosis, rather than by any change in the content of individual granules.     

Duodenal ulcer disease: Helicobacter pylori and hyperchlorhydria

Basal and pentagastrin-stimulated gastric acid secretion and basal serum gastrin level were investigated in 55 active duodenal ulcer patients with antral colonization with Helicobacter pylori (HP) and 17 patients without. Our study shows that basal (BAO) and pentagastrin-stimulated gastric acid secretion (MAO and PAO) were significantly higher in HP positive than in HP negative patients with duodenal ulcer disease. There were also a tendency to increase in basal serum gastrin concentration in HP positive patients. We suggest that antral HP increases antral gastrin release and gastric secretion. Increased acid secretion then causes duodenal ulcers by producing a low intraduodenal pH.     

Mechanism of action of the calcium-sensing receptor in human antral gastrin cells

BACKGROUND AND AIMS: Human G cells express the calcium-sensing receptor and respond to extracellular calcium by releasing gastrin. However, the receptor on G cells is insensitive to serum calcium levels. We investigated whether this is a result of differential regulation of signaling pathways compared with parathyroid or calcitonin cells. METHODS: Gastrin release from primary cultures of human antral epithelial cells enriched for G cells (35%) was measured by radioimmunoassay. G cells were stimulated by increasing extracellular calcium concentration for 1 hour in the presence or absence of antagonists of specific intracellular signaling pathways. Intracellular calcium levels were monitored to evaluate the effect of the antagonists on calcium influx. RESULTS: Inhibition of phospholipase C decreased calcium-stimulated gastrin release, but blockers of adenylate cyclase, phospholipase A(2), or mitogen-activated protein kinase had no effect. Inhibition of protein kinase C, nonselective cation channels, and phosphodiesterase increased basal and calcium-stimulated gastrin release while decreasing calcium influx. These data were consistent with basally active phosphodiesterase. CONCLUSIONS: The calcium-sensing receptor on the G cell activates phospholipase C and opens nonselective cation channels, resulting in an influx of extracellular calcium. Protein kinase C isozymes expressed by the G cells play multiple roles regulating both gastrin secretion and phosphodiesterase activity.     

G cell population of the gastric antrum, plasma gastrin, and gastric acid secretion in patients with and without duodenal ulcer.

Estimates of the G cell population were made in 24 resected human pyloric antra from counts of cells in multiple samples and from measurements of antral size. Measurements had been made previously in 20 subjects of acid output (basal and after pentagastrin) and in 10 subjects of plasma gastrin (basal and after insulin + bicarbonate). G cells were most dense near the pylorus, but their circumferential distribution was even. The G cell populations ranged from 8 to 15 (mean 10) million in four control patients and from 3 to 43 (mean 18) million in 15 patients with duodenal ulcer. Those with recurrent ulcer after vagotomy had either a low G cell count and incomplete vagotomy, or a high G cell count and apparently complete denervation. Two patients with hypergastrinaemia and duodenal ulcer had moderate (29 X 10(6)) or marked (56 X 10(6)) excesses of G cells. 'G cell hyperplasia' may represent the extreme end of the normal range of G cell numbers in the antrum, and can be assessed by semi-quantitative grading of G cell hyperplasia in antral biopsies. There were significant direct correlations between antral area and G cell density, between peak acid output and G cell population, and between basal plasma gastrin and G cell density (but not population). We suggest that, in patients with duodenal ulcer, acid and gastrin secretion are interrelated and that both are related to the masses of parietal cells and of G cells.     

Interactions between antral peptides and prostaglandin biosynthesis in gastric acid regulation in man

The role of endogenous prostaglandins as modulators of antral hormone release and gastric acid secretion was studied in the intact human stomach. The subjects (n = 9) received indomethacin prior to gastric perfusion at pH greater than 7 or less than 2 and subsequent vagal stimulation. Indomethacin was also tested against parenteral somatostatin (n = 10) and pentagastrin (n = 8). The release of somatostatin into the circulation was biphasic after vagal stimulation, and the plasma levels were inversely proportional to those of plasma gastrin. Acidification of the gastric antrum from pH greater than 7 to less than 2 increased twofold the basal plasma levels of somatostatin (p less than 0.05) and suppressed basal and vagally stimulated gastrin release (p less than 0.05) and gastric acid secretion (p less than 0.05). Indomethacin prior to acidification had little effect in the basal state. Following stimulation the release of somatostatin increased, as indicated by a twofold elevation of somatostatinlike immunoreactivity in the gastric lumen (p less than 0.05), but there was less inhibition of plasma gastrin (p less than 0.05) and gastric acid secretion (p less than 0.05) as compared to acidification alone. During alkaline gastric perfusion, indomethacin increased circulating somatostatin (p less than 0.05) levels without affecting plasma gastrin or gastric acid. Indomethacin given against intravenously infused somatostatin (0.1 microgram.kg-1.h-1) partially reversed the inhibited gastrin response to vagal stimulation without affecting somatostatin-suppressed gastric acid secretion. The effects of indomethacin against pentagastrin were marginal. In conclusion: Gastric acidification in man stimulates plasma release of somatostatin in parallel to suppressing gastrin release and gastric acid secretion. Endogenous prostanoids participate to regulate antral hormone interactions and may have dual actions on antral somatostatin, as negative modulators of release and as mediators of somatostatin effects on the gastrin cell. It is suggested that an unrestricted release of antral somatostatin is reflected in the gastric lumen rather than in the circulation.     

Antral release of gastrin and somatostatin in duodenal ulcer and control subjects.

Organ culture was used to compare gastrin and somatostatin release from cultured antral mucosa obtained from duodenal ulcer and non-ulcer (control) subjects. In response to dibutyryl cyclic AMP (DBCAMP) cultured antral mucosal explants from patients with a history of duodenal ulcer released a greater proportion of antral gastrin into the medium than did antral mucosal explants from non-ulcer subjects. Somatostatin release from antral mucosa from duodenal ulcer patients was substantially less than somatostatin released by antral explants from non-ulcer subjects. In the non-ulcer subjects there was a direct positive correlation between the amounts of antral somatostatin and gastrin released into the culture medium (r = 0.64, less than p 0.01). In the duodenal ulcer patients, however, there was no correlation between gastrin release and somatostatin release from antral mucosa ( r = 0.09; p greater than 0.2). Results of these studies identify enhanced gastrin release in response to stimulation and decreased release of somatostatin from antral mucosa of duodenal ulcer patients. These alterations in paracrine relationships of antral somatostatin and gastrin in duodenal ulcer subjects may contribute, at least in part, to the pathogenesis of duodenal ulcer disease.     

Gastrointestinal hormone abnormalities and G and D cells in functional dyspepsia patients with gastric dysmotility

AIM: To investigate the relationship between gastric dysmotility, gastrointestinal hormone abnormalities, and neuroendocrine cells in gastrointestinal mucosa in patients with functional dyspepsia (FD). METHODS: Gastric emptying was assessed with solid radiopaque markers in 54 FD patients, and the patients were divided into two groups according to the results, one with delayed gastric emptying and the other with normal gastric emptying. Seventeen healthy volunteers acted as normal controls. Fasting and postprandial plasma levels and gastroduodenal mucosal levels of gastrointestinal hormones gastrin, somatostatin (SS) and neurotensin (NT) were measured by radioimmunoassay in all the subjects. G cells (gastrin-producing cells) and D cells (SS-producing cells) in gastric antral mucosa were immunostained with rabbit anti-gastrin polyclonal antibody and rabbit anti-SS polyclonal antibody, respectively, and analyzed quantitatively by computerized image analysis. RESULTS: The postprandial plasma gastrin levels, the fasting and postprandial plasma levels and the gastric and duodenal mucosal levels of NT were significantly higher in the FD patients with delayed gastric emptying than in those with normal gastric emptying and normal controls. The number and gray value of G and D cells and the G cell/D cell number ratio did not differ significantly between normal controls and the FD patients with or without delayed gastric emptying. CONCLUSION: Our findings suggest that the abnormalities of gastrin and NT may play a role in the pathophysiology of gastric dysmotility in FD patients, and the abnormality of postprandial plasma gastrin levels in FD patients with delayed gastric emptying is not related to the changes both in the number and gray value of G cells and in the G cell/D cell number ratio in gastric antral mucosa.     

Role of calcium in the stimulus-secretion coupling of antral gastrin release

The role of calcium in the stimulus-secretion coupling of antral gastrin release was examined in isolated sheets of canine antral mucosa. Mucosa was obtained from 137 dogs and mounted in Ussing chambers to separate the luminal from nutrient surfaces. The influence of verapamil, LaCl3, A23187, and EGTA on the release of gastrin by luminal calcium and ethyl alcohol was examined and the release of immunoreactive gastrin (IG) was measured in luminal perfusates. Release of IG by luminal calcium was dose-related, unsaturable, and impaired by verapamil and by LaCl3. Release of IG by alcohol was prevented by leaching the mucosa of calcium and restored by repletion of the calcium. IG release induced by alcohol was prevented by topical, but not by nutrient, application of LaCl3. Molecular sieve and affinity chromatography of the endogenous IG released in the absence of luminal calcium, and of the exogenous gastrin added, indicated that antral gastrin was released as heptadecapeptide gastrin, and that which was released in the presence of CaCl2 degraded rapidly into a C-terminal fragment. The data indicate that calcium may participate in the stimulus-secretion coupling of canine antral gastrin release in vitro.     

Tumour necrosis factor alpha antibody affects gastrin release in Crohn disease

BACKGROUND: Gastrin plays an important role in the regulation of gastric acid secretion in humans. Tumour necrosis factor alpha (TNF-alpha) stimulates gastrin release from antral G cells in vitro. The aim was to determine whether gastrin release decreases in patients with Crohn disease treated with monoclonal antibody to TNF-alpha. METHODS: Twenty-five consecutive patients with Crohn disease (10 M, 15 F; 18 with fistulas) were treated with a single intravenous infusion of the monoclonal antibody to TNF-alpha, infliximab, at a dose of 5 mg/kg. Basal and bombesin stimulated gastrin was measured after an overnight fast immediately before and 2 weeks after infliximab. Helicobacter pylori status was determined by serology. RESULTS: Twenty-two patients were H. pylori-negative. Basal plasma gastrin was 21 (16-26) pmol/L before and 19 (15-25) pmol/L after infliximab (NS). Bombesin stimulated gastrin decreased from 49 (40-62) pmol/L before to 36 (33-59) pmol/L (P < 0.005) 2 weeks after infliximab. CONCLUSION: Gastrin release in response to bombesin decreases in patients with Crohn disease treated with infliximab.     

Effect of systemic gastric acid stimulation and intragastric pH changes on synchronous antral gastrin and somatostatin release in anesthetized,nonatropinized duodenal ulcer patients and controls

The synchronous changes in antral gastrin and somatostatin release in anesthetized, nonatropinized duodenal ulcer patients and control subjects were investigated by serial intraoperative blood sampling from the right gastroepiploic vein. The mean basal antral plasma gastrin and somatostatin concentrations of the two groups did not differ significantly. The significantly greater gastric acid secretory response to systemic gastric acid stimulation (pentagastrin stimulation) in duodenal ulcer patients compared with that of control subjects was not linked to any difference in antral somatostatin release pattern. The decrease in antral plasma gastrin release was significantly lower after acid instillation and the increase was significantly higher after alkali instillation in duodenal ulcer patients compared with those of controls, indicating an abnormal gastrin response to intragastric pH changes in duodenal ulcer patients, which was again not found to be coupled to any significant difference in antral somatostatin release. The results suggest that an abnormal somatostatin-mediated inhibition of gastrin release and/or gastric acid secretion does not exist in duodenal ulcer patients.     

幽门螺杆菌感染对十二指肠溃疡和功能性消化不良患者胃G细胞功能的影响

目的探讨幽门螺杆菌(Helicobacterpylori,Hp)感染及溃疡灶对胃窦部G细胞功能的影响。方法活动性十二指肠溃疡(DU)77例根据Hp情况分为A组Hp根除组51例,男37例,女14例,年龄为(35．2±12．6)岁;B组Hp持续阳性12例,男9例,女3例,年龄为(34．5±10．3)岁;C组Hp阴性14例,男9例,女5例,年龄为(37．5±11．8)岁。D组为Hp根除的功能性消化不良(FD)25例,男15例,女10例,年龄为(38．1±12．6)岁。治疗前后检查内镜,取胃窦黏膜观察G细胞数量(ABC法免疫组化)、胃泌素基因表达(32P-dATP掺入RT-PCR),血浆胃泌素采用RIA测定。结果各组G细胞数量比较,差异无显著性(P>0．05)。治疗前各DU组(A、B、C组)胃泌素基因表达水平高于FD组(D组)(P<0．01)、Hp阳性DU组(A、B组)与Hp阴性DU组(C组)相似(P>0．05)。治疗后各DU组(A、B、C组)胃泌素基因表达、血浆胃泌素水平有下降趋势,但差异无显著性(P>0．05),而FD组水平均低于根除前(P<0．05)。治疗前FD组胃泌素水平与DU组相似(P>0．05),Hp根除后胃泌素水平低于各DU组(P<0．001)。血浆胃泌素水平与胃泌素基因表达水平正相关(P<0．05)。结论Hp感染不影响胃G细胞数量,但可促进胃泌素基因表达和胃泌素释放,Hp根除后胃泌素水平降低;溃疡灶可使胃泌素过度释放。     

Appearance of gastrin and somatostatin in the human fetal stomach, duodenum and pancreas.

The gestational time of appearance of gastrin and somatostatin in the human fetal stomach, duodenum and pancreas was examined. Immunoreactive gastrin (IRG) is detected in antral, duodenal and pancreatic extracts of a 7.0-cm (crown-heel length) fetus. More IRG is extracted from the duodenum than the antrum. Duodenal IRG concentration from fetuses of 16.0--26.0 cm are higher than younger fetal and adult concentrations. Antral IRG concentrations are one tenth of the adult contents. Very small IRG concentrations are present in the human fetal pancreas. Gastrin immunohistochemical staining is positive first in duodenal (6.5-cm fetus) and later in antral (12.5-cm fetus) mucosa; pancreatic tissue is negative for gastrin immunohistochemistry. Type IV cells are encountered in antral and duodenal mucosa of 4.0-cm fetuses; other endocrine cells appear with fetal growth. Not until much later in gestation (21.0 cm) do typical G cells appear. These results suggest that early in fetal life gastrin is produced by the type IV cell. Somatostatin immunohistochemical staining is positive in stomach, duodenum and pancreas in 6.5-cm fetuses. Immature D cells are found in antral and duodenal mucosa of 5.0-cm fetuses and mature D cells in 11.0-cm fetuses.