Somatostatin inhibition of basal and carbachol-stimulated gastrin release in rat antral organ culture

The effects of somatostatin on gastrin release and total gastrin immunoreactivity were examined under in vitro conditions in rat antral organ culture experiments. Basal antral gastrin release was inhibited by somatostatin. Total culture gastrin contents (culture medium gastrin plus extracted antral mucosal gastrin) at 6 h were reduced significantly by 10(-5) M (p less than 0.02) and 10(-4) M (P less than 0.01) somatostatin. Gastrin release into the culture media stimulated by the cholinergic agent, carbachol (10(-5) M), was suppressed by somatostatin: at 30 min and 6 h of culture 10(-8) M somatostatin inhibited carbachol-stimulated gastrin release by 66% and 54%, respectively, and 10(-5) M and 10(-4) M somatostatin completely abolished gastrin release. The rate of gastrin release stimulated by carbachol was suppressed significantly by each dose of somatostatin examined (10(-8) M to 10(-4) M). The present studies indicate that somatostatin inhibits both gastrin secretion by cultured rat antral mucosa and total antral culture gastrin contents, and demonstrate that cholinergically-mediated gastrin secretion is inhibited by somatostatin.     

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.     

The effects of peptide histidine isoleucine on antral gastrin and somatostatin.

The present studies were directed to determine whether peptide histidine isoleucine (PHI) affects expression of the gastrin and somatostatin genes and whether such effects may be functionally linked. In separate experiments, the effects of PHI on medium gastrin and somatostatin concentrations, the incorporation of 35S-labelled amino acids into newly synthesized gastrin and somatostatin, and steady state gastrin and somatostatin mRNA were determined. PHI inhibited basal expression of the gastrin gene at all levels examined, while no significant effect on basal somatostatin gene expression could be detected. PHI also decreased carbachol-stimulated antral gastrin release and simultaneously increased somatostatin release. However, in contrast to its structural analogues, secretin and gastric inhibitory peptide, the immunoneutralization of endogenous somatostatin by the administration of specific antibodies did not affect significantly the capacity of PHI to inhibit gastrin release into the culture medium stimulated by carbachol. The results of these studies indicate that PHI exerts a physiological inhibitory effect on antral gastrin cells and that this inhibition may occur at several steps along the biosynthetic pathway. In addition, unlike its structural analogues, PHI inhibition of carbachol-stimulated gastrin release is not functionally linked to its stimulatory effects on somatostatin release.     

Postreceptor inhibition of antral gastrin release by somatostatin

This study was performed to examine the effects of somatostatin on antral gastrin release stimulated by postreceptor increases in adenosine cyclic nucleotide. Increases in intracellular levels of cyclic adenosine monophosphate were achieved through the use of the dibutyryl derivative of cyclic adenosine monophosphate and the phosphodiesterase inhibitor theophylline. The effects of somatostatin on basal and stimulated gastrin release were examined in rat antral organ culture experiments. Inclusion of somatostatin in the culture medium (1 X 10(-8) to 1 X 10(-4) M) resulted in significant inhibition of gastrin release at somatostatin concentrations of 1 X 10(-5) and 1 X 10(-4) M: both doses of somatostatin inhibited gastrin release by approximately 52% at 30 min and by 32% at 6 h. Gastrin release stimulated by dibutyryl cyclic adenosine monophosphate was significantly inhibited by 1 X 10(-5) and 1 X 10(-4) M somatostatin to 133% and 121% at 30 min and 77% and 98% at 6 h, respectively. Gastrin release stimulated by theophylline (1 mM) was also significantly inhibited by somatostatin in doses ranging from 1 X 10(-6) to 1 X 10(-4) M. The degree of inhibition by somatostatin of dibutyryl cyclic adenosine monophosphate- and theophylline-stimulated gastrin release declined over the duration of culture. In conclusion, these results suggest that somatostatin inhibits adenosine cyclic nucleotide-stimulated gastrin release by acting at a point distal to the formation of cyclic adenosine monophosphate.     

Effect of intragastric pH on antral gastrin and somatostatin release in anaesthetised, atropinised duodenal ulcer patients and controls.

The synchronous change in the antral release of gastrin and somatostatin into a vein draining the stomach was studied during acidic and alkaline intragastric pH in six anaesthetised duodenal ulcer patients and six controls after atropinisation. No differences in the basal secretion of gastrin and somatostatin were observed among the two groups. Alkaline as well as acidic intragastric pH had no effect on the antral release of somatostatin in duodenal ulcer patients and controls. In contrast, alkaline intragastric pH was associated with a significantly higher antral gastrin release in duodenal ulcer patients than in controls. Acidic intragastric pH was associated with a significantly smaller inhibition of antral gastrin release in duodenal ulcer patients than in controls. These results suggest that atropinised anaesthetised duodenal patients release gastrin abnormally in the presence of acidic or alkaline intragastric pH and that any inverse relationship between antral gastrin and somatostatin release is uncoupled under these conditions.     

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.     

Effects of carbachol on gastrin and somatostatin release in rat antral tissue culture

Recent studies have demonstrated that somatostatin-containing cells are in close anatomic proximity to gastrin-producing cells in antral mucosa, suggesting a potential local regulatory role for somatostatin. The purpose of this study was to examine further the relationships between gastrin and somatostatin and the effects of the cholinergic agonist carbachol on content and release of gastrin and somatostatin using rat antral mucosa in tissue culture. Antral mucosa was cultured at 37 degrees C in Krebs-Henseleit buffer, pH 7.4, gassed with 95% O2-5% CO2. After 1 h, the culture medium was decanted and the tissue was boiled to extract mucosal gastrin and somatostatin. Inclusion of carbachol 2.5 X 10(-6) M in the culture medium decreased medium somatostatin from 1.91 +/- 0.28 (SEM) ng/mg tissue protein to 0.62 +/- 0.12 ng/mg (p less than 0.01), extracted mucosal somatostatin from 2.60 +/- 0.30 to 1.52 +/- 0.16 ng/mg (p less than 0.001), and percentage of somatostatin released from 42% +/- 2.6% to 27% +/- 2.2% (p less than 0.01). Carbachol also increased culture media gastrin from 14 +/- 2.5 to 27 +/- 3.0 ng/mg protein (p less than 0.01). Tissue content and release of gastrin and somatostatin were also examined during culture of rat antral mucosa in culture media containing antibodies to somatostatin in the presence and in the absence of carbachol. Incubation with somatostatin antisera, both with and without carbachol, markedly increased culture media concentrations of somatostatin, all of which was effectively bound by antibodies present in the media. Antibody binding of somatostatin was accompanied by significant increases in culture media gastrin concentrations, both in the presence and in the absence of carbachol. Results of these studies support the hypothesis that antral somatostatin exerts a local regulatory effect on gastrin release and that cholinergic stimulation of gastrin release is mediated, at least in part, through inhibition of somatostatin synthesis and release.     

Influence of chronic drug-induced achlorhydria by substituted benzimidazoles on the endocrine stomach in rats

The release of gastric somatostatinlike immunoreactivity and gastrin was studied in rats with chronic achlorhydria induced by the substituted benzimidazole BY 308. In vitro, stimulation of gastrin release by acetylcholine was slightly enhanced after 1 day of treatment but no further effects were observed compared to placebo controls. Four weeks of treatment evoked marked gastrin hypersecretion, which was atropine-resistant. Stimulation of gastrin release was inversely correlated to enhancement of basal gastrin levels. Chronic achlorhydria distinctly reduced somatostatin responses to isoproterenol, whereas potent stimulation was observed in controls. Treatment with BY 308 for 1 wk was associated with fully developed gastrin hypersecretion but isoproterenol-stimulated somatostatin release was still unaffected. Hypergastrinemia accompanied by increased antral gastrin and reduced antral and fundic somatostatin concentrations was also found in vivo after 4 wk of treatment with BY 308. It is concluded that chronic achlorhydria not only enhances storage and secretion of gastrin but also diminishes the secretion and tissue stores of somatostatin; adaptive changes of the somatostatin cell occur, however, with a much longer delay.     

Cholecystokinin inhibits gastrin secretion independently of paracrine somatostatin secretion in the pig

BACKGROUND: Cholecystokinin inhibits the secretion of gastrin from antral G cells, an effect that is speculated to be mediated by D cells secreting somatostatin. The aim of the study was to test directly whether cholecystokinin inhibition of antral gastrin secretion is mediated by somatostatin. METHODS: The effects of CCK on gastrin and somatostatin secretion were studied in isolated vascularly perfused preparations of pig antrum before and after immunoneutralization brought about by infusion of large amounts of a high affinity monoclonal antibody against somatostatin. RESULTS: CCK infusion at 10(-9) M and 10(-8) M decreased gastrin output to 70.5% +/- 7.6% (n = 8) and 76.3% +/- 3.6% (n = 7) of basal output, respectively. CCK at 10(-10) M had no effect (n = 6). Somatostatin secretion was dose-dependently increased by CCK infusion and increased to 268 +/- 38.2% (n = 7) of basal secretion during infusion of CCK at 10(-8) M. Immunoneutralization of somatostatin caused a doubling of the basal secretion of gastrin, but did not affect the CCK-induced decrease in gastrin secretion. CONCLUSION: CCK inhibits gastrin secretion independently of paracrine somatostatin secretion.     

Effect of glucagon-like peptide-1 on gastric somatostatin and gastrin secretion in the rat

The effect of glucagon-like peptide-1 (GLP-1) amide on gastric somatostatin and gastrin secretion was investigated in the isolated, vascularly perfused rat stomach preparation. GLP-1 (7-36) amide, 10(-12) to 10(-7)M, dose-dependently increased gastric somatostatin release, achieving maximal stimulation (314 +/- 15% above basal) at the highest dose. The somatostatin response to 10(-8)M GLP-1 (7-36) amide was not affected by concomitant perfusion with tetrodotoxin. GLP-1 (1-36) amide did not affect somatostatin release. Both basal and acetylcholine-stimulated gastrin were inhibited by GLP-1 (7-36) amide but were not influenced by GLP-1 (1-36) amide. In is concluded that GLP-1 (7-36) amide is the biologically effective peptide that stimulates gastric somatostatin and inhibits gastrin secretion, probably via non-neural pathways. GLP-1 (7-36) amide-induced inhibition of gastric acid secretion may, at least in part, be due to enhanced somatostatin and/or decreased gastrin release.     

Cholinergic mediation of gamma-aminobutyric acid-induced gastrin and somatostatin release from rat antrum

Addition of gamma-aminobutyric acid (GABA) to antral mucosal fragments in short-term incubation results in dose-dependent and bicuculline-sensitive stimulation of gastrin release and inhibition of somatostatin release, respectively. These effects of GABA on antral gastrin and somatostatin release closely resembled the actions of cholinergic agonists on G- and D-cell function. The present study examines the possibility that the effects of GABA on antral peptide release may be mediated, in part, through stimulation of antral cholinergic neurons. Inclusion of either atropine or pirenzepine in incubation medium prevented GABA-induced stimulation of gastrin release and inhibition of somatostatin release. Addition of the acetylcholinesterase inhibitor, physostigmine, caused a leftward shift in the GABA dose-response curve and increased by 10-fold the sensitivity of the antral preparation to GABA stimulation. Studies with tetrodotoxin suggest that GABA-stimulated gastrin release is mediated through activation of neurons contained within the antral mucosal/submucosal fragments. Hexamethonium, the ganglionic nicotinic receptor antagonist, did not affect GABA-induced gastrin release. These results indicate that GABA affects antral gastrin and somatostatin release through stimulation of antral postganglionic cholinergic neurons.     

Role of gastrin in bombesin-stimulated somatostatin release

The intermediary pathways in the bombesin-induced somatostatin release were examined in isolated perfused rat stomach obtained from male rats that were fasted overnight. The stomachs were perfused by way of the celiac artery. On coinfusion of 1.0 mumol/L tetrodotoxin and 1 nmol/L bombesin, a significant depression in release of somatostatin was observed compared with that observed with bombesin alone. The 5-minute integrated somatostatin response after treatment with tetrodotoxin and bombesin was 173% +/- 14% of basal, which was significantly lower than that observed with bombesin alone (394% +/- 59% of basal, P less than 0.05) but significantly higher than that observed with medium-199 alone (95% +/- 7% of basal, P less than 0.05); this indicated that approximately 70% of the bombesin-stimulated somatostatin release was indirectly mediated through neural pathways, while a significant (approximately 30%) segment of it was mediated by nonneural mechanisms. To test if the 30% somatostatin release was secondary to gastrin release in response to bombesin, gastrin antiserum and bombesin (1 nmol/L) were coadministrated in the presence or absence of tetrodotoxin (1 mumol/L). Gastrin antiserum alone did not significantly affect basal release of somatostatin but caused a significant inhibition (approximately 23%) of bombesin-provoked somatostatin release. Coadministration of gastrin antiserum and tetrodotoxin attenuated bombesin-stimulated somatostatin release. Gastrin (1 mumol/L) alone significantly stimulated somatostatin release (150% +/- 10% of basal), which was completely attenuated in the presence of gastrin antiserum. Tetrodotoxin did not affect bombesin-elicited gastrin release, confirming that bombesin-stimulated gastrin release was directly mediated. To determine the nature of the neural pathways mediating the bombesin-induced somatostatin release, atropine (100 nmol/L) was used. Atropine inhibited bombesin-induced somatostatin release to the same extent as tetrodotoxin, indicating that cholinergic pathways mediated bombesin-induced somatostatin release. These results show that almost all the somatostatin response to bombesin is indirectly mediated, and is composed of a major neural (cholinergic) and a minor nonneural pathway. The nonneural mechanism appears to be contributed primarily by gastrin released in response to bombesin, which apparently has a short paracrine positive feedback effect on somatostatin release.     

Effect of environmental hyperthermia on gastrin, somatostatin and motilin in rat ulcerated antral mucosa

AIM: To study the effect of environmental hyperthermia on gastrin, somatostatin and motilin in rat ulcerated antral mucosa.METHODS: Forty-two Wistar rats were equally divided into six groups, according to the room temperature (high and normal) and the treatment (acetic acid, normal saline and no treatment). Levels of gastrin, somatostatin and motilin in rat ulcerated antral mucosa were measured with a radioimmunoassay method.RESULTS: The average temperature and humidity were 32.5℃ and 66.7% for the high temperature group, and 21.1℃ and 49.3% for the normal temperature group,respectively. Gastric ulcer model was successfully induced in rat injected with 0.05 mL acetic acid into the antrum. In rats with gastric ulcers, the levels of gastrin and motilin increased, whereas the somatostatin level declined in antral mucosa, compared with those in rats treated with normal saline and the controls. However, the change extent in the levels of gastrin, motilin and somatostatin in antral mucosa was less in the high temperature group than in the normal temperature group.CONCLUSION: The levels of gastrin, somatostatin and motilin in rat ulcerated antral mucosal tissue remain relatively stable in a high temperature environment, which may relate to the equilibration of the dynamic system.     

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.     

Participation of antral somatostatin in the local regulation of gastrin release

In anaesthetized pigs gastrin release was stimulated by irrigation of the antrum with bicarbonate and by instillation of a meat extract. The concentration of gastrin and somatostatin was measured by radioimmunoassay both in the antral and peripheral venous blood. The increase in gastrin was coupled to a significant decrease in somatostatin immunoreactivity as measured in the antral venous blood both during instillation of alkali and meat extract. In peripheral blood, the differences were much less evident and not statistically significant. It is speculated that the decrease in release of antral somatostatin during alkalinization and instillation of meat extract is the primary event which is followed by a diminished inhibition of gastrin liberation. Thus, the present data support the hypothesis that antral somatostatin participates in the local regulation of gastrin release.     

Cholecystokinin inhibits gastrin secretion independently of paracrine somatostatin secretion in the pig

Background: Cholecystokinin inhibits the secretion of gastrin from antral G cells, an effect that is speculated to be mediated by D cells secreting somatostatin. The aim of the study was to test directly whether cholecystokinin inhibition of antral gastrin secretion is mediated by somatostatin. Methods: The effects of CCK on gastrin and somatostatin secretion were studied in isolated vascularly perfused preparations of pig antrum before and after immunoneutralization brought about by infusion of large amounts of a high affinity monoclonal antibody against somatostatin. Results: CCK infusion at 10 ^?9 M and 10 ^?8 M decreased gastrin output to 70.5%?±?7.6% (n?=?8) and 76.3%?±?3.6% (n?=?7) of basal output, respectively. CCK at 10 ^?10 M had no effect (n?=?6). Somatostatin secretion was dose‐dependently increased by CCK infusion and increased to 268?±?38.2% (n?=?7) of basal secretion during infusion of CCK at 10 ^?8 M. Immunoneutralization of somatostatin caused a doubling of the basal secretion of gastrin, but did not affect the CCK‐induced decrease in gastrin secretion. Conclusion: CCK inhibits gastrin secretion independently of paracrine somatostatin secretion.     

Effects of calcium on cholinergic-stimulated gastrin release in the rat

The effects of alterations in availability and access of extracellular media calcium on antral gastrin release were examined in the basal state and in response to cholinergic stimulation in rat antral organ culture experiments. In the presence of either divalent cationic chelator (EGTA) or calcium channel blocker (verapamil, nifedipine), carbachol-stimulated gastrin release was inhibited completely to values that were not significantly different from non-stimulated control. In the absence of added calcium chloride, carbachol stimulated gastrin release during the initial 30 min of culture but not at 60 and 120 min of culture. Inhibition by EGTA and verapamil of carbachol-stimulated gastrin release during the initial 30 min of culture suggests, but does not prove, that these agents may also affect intracellular availability and movement of calcium. Cholinergic stimulation of gastrin release demonstrated a concentration-dependent relationship with extracellular calcium: optimal culture media calcium concentration was 1 mM. In conclusion, these studies indicate that cholinergic stimulation of the gastrin cell requires availability of extracellular calcium.     

Effects of somatostatin and acid on inhibition of gastrin release in newborn rats

Newborn dogs, humans, and rats have elevated gastric luminal pH values and significantly elevated serum gastrin levels compared to adults. In the adult, acidification of the antral mucosa to pH 3.0 or lower inhibits gastrin release. Somatostatin is released by acid and may mediate this effect. We examined the effects of gastric acidification and somatostatin injection in rats aged 10 days to adult. Gastric gavage with 0.15 M HCl significantly lowered serum gastrin in animals of all ages. Somatostatin injection (400 micrograms/kg) significantly decreased serum gastrin in rats aged 18 days or older, but not in 10- and 15-day-old animals. These data indicate that 1) the mechanism whereby antral acidification inhibits gastrin release is at least partially developed in unweaned rats, 2) somatostatin is not a necessary mediator of the inhibition of gastrin release, and 3) at least part of the hypergastrinemia found in newborn animals is of antral origin.     

Somatostatin is an essential paracrine link in acid inhibition of gastrin secretion.

We studied the functional coupling between antral somatostatin and gastrin cells in pigs using isolated perfused preparations of the antrum with intact supply of the vagus nerves. Luminal acidification significantly inhibited gastrin secretion to 61 +/- 3% of basal secretion and increased somatostatin output 9-fold. Intra-arterial infusion of somatostatin to concentrations of 10(-10) and 10(-9) mol/l inhibited gastrin secretion to 18 +/- 9 and 33 +/- 11% of basal secretion. Electrical stimulation of the vagus nerves and intra-arterial infusion of gastrin-releasing polypeptide (GRP; 10(-9) mol/l) significantly increased both gastrin and somatostatin secretion. Addition to the perfusate of Fab fragments of somatostatin antibodies abolished the effect of somatostatin at 10(-10) mol/l and the acid inhibition of gastrin secretion, but had no effect on the response to vagus stimulation of GRP infusion. We conclude that a local release of somatostatin is essential for the acid-induced inhibition of gastrin secretion, whereas changes in the local somatostatin concentration are unlikely to play a major role in vagally or GRP-induced gastrin secretion.