Effects of glucagon, secretin, and vasoactive intestinal polypeptide on gastric somatostatin and gastrin release from isolated perfused rat stomach

To investigate the role of gastric somatostatin on gastrin secretion, glucagon, secretin, and vasoactive intestinal polypeptide (VIP) were perfused in the isolated pancreas-spleen-duodenum deprived preparation of rat stomach. After a preperfusion with 4.6% dextran Krebs-Ringer bicarbonate buffer containing 5.5 mM glucose, glucagon, secretin, and VIP at the concentrations of 10(-8), 10(-7), and 10(-6) M were infused into the left gastric artery at a constant flow of 2 ml/min for 15 min. All glucagon, secretin, and VIP evoked dose-dependent increases of somatostatin secretion with a simultaneous dose-related decrease of gastrin release. Furthermore, a significant correlation was found between the increase of somatostatin release and the decrease of gastrin secretion induced by glucagon, secretin, and VIP. These results raise the possibility that the suppression of gastrin secretion induced by glucagon, secretin, and VIP may, at least in part, be mediated by local action of gastric somatostatin.     

Adrenergic control of rat gastric somatostatin and gastrin release

The effect of adrenergic agonists and antagonists on the secretion of gastric somatostatin-like immunoreactivity (SLI) and gastrin was investigated in an isolated, vascularly perfused rat stomach preparation. Two- to six-fold increases in SLI secretion induced by isoproterenol, epinephrine, and norepinephrine were completely abolished by propranolol but were not influenced by phentolamine. Propranolol did not alter glucagon- and DB-cAMP-induced stimulation of SLI release. Experiments in which the beta 2-agonist salbutamol and the beta 1- and beta 2-blockers practolol and H35/25 were used showed that both subtypes of beta receptors are involved. Gastrin secretion revealed only minor changes in dose-response studies with a wide range of isoproterenol concentrations (2 X 10(-8) to 1.5 X 10(-4) M). The results obtained in this study suggest that in rats 1) the SLI response to adrenergic agonism is predominantly mediated by beta receptors; 2) both beta 1- and beta 2-adrenergic receptors are involved; 3) under in vitro conditions, adrenergic agonism is a weak stimulus for gastrin secretion.     

Effect of gastrin receptor antagonists on gastric acid secretion and gastrin and somatostatin release in the rat stomach.

The effects of two recently developed gastrin receptor antagonists, PD 136450 and L-365,260, on pentagastrin-stimulated acid secretion were investigated in rats. PD 136450 at a dose of 6 mg/kg s.c. (9.6 mumol) completely abolished acid secretion induced by pentagastrin. The inhibition of 18 mg/kg PD 136450 s.c. lasted for at least 8 h and was still effective after 14 days of treatment (18 mg/kg s.c. every 8 h). Acute application of L-365,260 at a dose of 3.8 mg/kg, which is equimolar (9.6 mumol) to 6 mg/kg PD 136450 reduced acid responses slightly. However, when L-365,260 was administered intravenously at a dose of 3 mg/kg, this antagonist completely abolished the pentagastrin-stimulated acid secretion. Furthermore, the effect of PD 136450 on endogenous gastric somatostatin and gastrin releases was tested in the isolated, vascularly perfused rat stomach. PD 136450 perfused at a concentration of 1 microM slightly increased somatostatin secretion after stimulation with a high dose of isoproterenol (10(-7) M). There was no effect of PD 136450 on basal or acetylcholine-stimulated gastrin secretion.     

Effects of aging on gastrin and somatostatin secretion from isolated perfused rat stomach

We have examined the release of gastrin and somatostatin from the isolated perfused stomach of rats of three different age groups (4 months, 12 months, and 24 months old) in response to bombesin and carbachol. The basal release of gastrin was diminished in 24-month-old rats. Basal somatostatin release showed an age-related decrease. Bombesin (10^–10 and 10^–9 M) and carbachol (10^–8 and 10^–7 M) stimulated gastrin release in each age group. The integrated release of gastrin in response to bombesin (10^–10 and 10^–9 M) or carbachol (10^–8 M) did not differ among the three age groups, although integrated gastrin release in response to carbachol (10^–7 M) decreased in 24-month-old rats. Bombesin-stimulated release of somatostatin decreased in 12- and 24-month-old rats. Carbachol inhibited release of somatostatin in each age group. Compared with 4-month-old rats, the inhibition of somatostatin release by carbachol was less in 24-month-old rats at 10^–8 and 10^–7 M, and less in 12-month-old rats at 10^–7 M. The decreased basal gastrin secretion and well-preserved gastrin response were further confirmed in conscious aged rats tested by means of oral gavage with 10% peptone. Our findings indicate that gastrin response to the stimuli is well preserved with aging, whereas the response of somatostatin diminishes in an age-related manner. Aging has different effects on the release of gastrin and somatostatin from the rat stomach.Supported by grants from the National Institutes of Health (PO1 DK 35608, 5R37 DK 15241).     

Effect of antibodies to somatostatin on acid secretion and gastrin release by the isolated perfused rat stomach

The present studies were directed toward examining the effect of somatostatin on gastrin release and acid secretion by the isolated vascularly perfused rat stomach. Rat stomachs were perfused in situ with Krebs-Ringer bicarbonate buffer containing 10% ovine erythrocytes and gassed with 95% O2-5% CO2. Inclusion of pentagastrin in the perfusion buffer increased acid output from 2.2 +/- 0.4 microEq H+/h during control perfusion to 18.8 +/- 1.8 microEq H+/h (p less than 0.01). In order to determine the effect of somatostatin on acid secretion and gastrin release, specific antibodies to somatostatin were included in the perfusate. Inclusion of antibodies to somatostatin in the buffer without pentagastrin did not significantly enhance acid output; however, gastrin concentration in the portal venous effluent increased from 15.1 +/- 2.0 to 25.2 +/- 5.2 pg/ml at 45 min (p less than 0.05). When antibodies to somatostatin were perfused in the presence of pentagastrin, acid output increased by 32% to 24.9 +/- 1.2 microEq H+/h (p less than 0.05); however, no change in gastrin concentration over basal was detected in the portal effluent. Results of these studies indicate that the capacity of the isolated rat stomach to secrete acid permits direct assessment of factors involved in the regulation of acid secretion. Under the conditions of these experiments, gastric somatostatin inhibits basal gastrin release and directly inhibits pentagastrin-stimulated acid secretion without affecting gastrin release.     

Calcitonin gene-related peptide stimulates somatostatin release from isolated perfused rat stomach

Effect of calcitonin gene-related peptide (CGRP) on somatostatin release was investigated on the isolated perfused rat stomach. Perfusion with CGRP (0.1 nM-100 nM) caused a significant and dose-dependent increase in effluent somatostatin levels. The somatostatin response to CGRP was rapid in onset and reversible immediately after the cessation of CGRP infusion. These findings suggest that CGRP stimulates the release of gastric somatostatin, thereby modulating gastric functions in rat.     

Adrenergic and cholinergic interactions in rat gastric somatostatin and gastrin release

The interactions of adrenergic and cholinergic influences on the gastric D cell were studied using an isolated perfused rat stomach in vitro. The sevenfold increase in the release of somatostatin-like immunoreactivity (SLI) in response to isoproterenol (4 . 10(-8) M) was dose-dependently inhibited by acetylcholine (10(-5) to 10(-8) M) whereas gastrin levels increased in a dose-dependent manner. Both inhibition of stimulated SLI and augmentation of gastrin release were completely abolished by atropine (10(-6) M). Isoproterenol (8 . 10(-9) M)-induced stimulation of SLI secretion was not altered by atropine. Antral exclusion completely eliminated gastrin secretion but basal and beta-adrenergic stimulated SLI release was not influenced. It is concluded that (1) cholinergic agonism reverses the stimulatory action of adrenergic agonists on the D cell, and (2) SLI from the rat stomach in vitro originates almost exclusively in the fundic region.     

Inhibition by somatostatin of carbamylcholine-induced gastrin and glucagon release from the isolated perfused canine stomach.

At an arterial plasma concentration of 61 nmol/l (100 ng/ml) synthetic cyclic somatostatin completely abolished basal glucagon and gastrin release as well as carbamylcholine-induced glucagon and gastrin release from the isolated perfused dog stomach. These observations are compatible with the view that endogenous somatostatin previously reported to be released during vagal stimulation might be involved to explain the lack of gastric-glucagon response in this situation. They do not, however, rule out the alternative proposal that the dog fundic A-cell may simply be a non-innervated cell.     

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.     

Somatostatin and gastrin release from canine stomach

Somatostatin and gastrin release into the veins draining the stomach was studied in 27 anaesthetized dogs. Basal somatostatin-like immunoreactivity (SLI) in corpus veins (136 +/- 36 pg/ml) was significantly higher than in antrum veins (83 +/- 20 pg/ml; p less than 0.05) and the femoral artery (58 +/- 15 pg/ml; p less than 0.02). During peptone, pH 6.5, perfusion of the stomach, SLI concentration increased significantly in the corpus veins to approximately four times basal and in the antrum veins to three times basal, whereas SLI levels in the peripheral circulation remained constant. Peptone, pH 3.5, and sodium oleate did not stimulate gastric SLI. Gastric distension increased significantly SLI release from the corpus. In gel filtration studies 50%--70% of SLI from gastric vein plasma samples but greater than 90% from femoral artery samples eluted in the void volume of Sephadex G-25 columns. Gastrin secretion was stimulated significantly only by peptone, pH 6.5.     

Effect of peptide YY on gastric acid secretion, gastrin and somatostatin release in the rat

The influence of PYY on stimulated gastric acid secretion and the possible role of gastric somatostatin was measured in rats. PYY, infused intravenously at a dose of 800 pmol/kg/h, reduced pentagastrin (20.8 nmol/kg/h) stimulated gastric acid secretion by 34 +/- 3%, whereas in controls acid secretion remained constant throughout the 90 min observation period. In a second series the effect of PYY on the endogenous gastric somatostatin-like immunoreactivity and gastrin-release was tested in the isolated, vascularly perfused rat stomach. PYY perfused at concentrations of 10 pM to 100 nM did not change either somatostatin or gastrin secretion from the rat stomach in vitro. The study shows that PYY suppressed acid secretion in the rat. Endogenous somatostatin or gastrin is unlikely to mediate the inhibitory effect of PYY on acid production.     

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.     

Effects of somatostatin on gastric secretion and gastrin release in man.

Somatostatin, a recently synthesized hypothalamic growth hormone release-inhibiting factor (GIF), was used in the cyclic and linear form. In all subjects studied, the cyclic GIF inhibited gastrin secretion during basal conditions as well as during a standard food stimulus, with immediate rebound after the infusion was stopped. Similar responses were observed in a hypophysectomized patient, indicating that this effect of GIF was independent of suppression of growth hormone secretion. Cyclic and linear GIF, when administered in normal subjects during an infusion of synthetic human gastrin I, almost totally suppressed gastric secretion. The results indicate that GIF is a potent inhibitor of gastric secretion and gastrin release.     

Effects of H2-receptor antagonist on gastrin and somatostatin secretion of rat stomach

To investigate the effects of 14 days administration of H2-receptor antagonist (famotidine) on gastric gastrin and somatostatin secretion, bombesin and glucagon were perfused in the isolated pancreas-duodenum deprived rat stomach. Then serum gastrin concentration, gastric mucosal gastrin and somatostatin content, and gastric mucosal G-cell and D-cell numbers were examined. The 14 days administration of famotidine caused the significant increase of basal gastrin secretion, antral G-cell hyperplasia, high gastrin sensitivity to the stimulation by bombesin, and the low somatostatin sensitivity to the stimulation by glucagon. These facts would suggest that 14 days famotidine administration disturbed not only gastrin secretion but also somatostatin secretion. These results may contribute, at least in part, to the high recurrence of ulcers after withdrawal of H2-receptor antagonists.     

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.     

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.     

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.     

Vagal release of IR-VIP and IR-gastrin from the isolated perfused rat stomach

The effects of electrical stimulation of the vagus at varying pulse widths on the release of immunoreactive VIP (IR-VIP) and IR-gastrin have been investigated, using the isolated perfused rat stomach preparation. Electrical stimulation of vagal trunks at a pulse width of 0.1 msec duration yielded no change in basal IR-VIP levels whereas a pulse width of 5.0 msec produced a prompt sustained increase. Stimulation at either pulse width evoked gastrin release. Atropine blocked the vagal release of IR-gastrin but not IR-VIP whereas hexamethonium blocked both responses. Exogenously administered porcine VIP, at concentrations mimicking endogenously released levels, was used in an attempt to reproduce the effects observed by vagal stimulation. Exogenous VIP had no effect on gastrin or somatostatin-like tmmunoreactivity (SLI) release. These in vitro studies support a role for VIP as a neurotransmitter released from the stomach by low-threshold non-cholinergic vagal fibres, but involving autonomie ganglia.     

Effects of [Asu1,7]-eel calcitonin on gastric somatostatin and gastrin release.

Effects of [Asu1,7]-eel calcitonin on gastric somatostatin and gastrin secretion were studied by using the isolated perfused rat stomach. [Asu1,7]-eel calcitonin (10(-9)--10(-7)M) caused a simultaneous dose-dependent increase of gastric somatostatin release and decrease of gastrin secretion, with a significant correlation between these two. The demonstration of calcitonin stimulation of gastric somatostatin release raises the possibility of somatostatin-mediated suppression of gastrin secretion by calcitonin.     

Paradoxical effects of gastrin releasing peptide on gastrin release and gastric secretion in the rat

The effects of gastrin releasing peptide (GRP) on gastrin release and gastric secretion were studied in anesthetized rats. Intravenous infusion of GRP (1-16 micrograms/kg/hr) caused a dose-dependent increase in serum gastrin level, however, it had no effect on basal gastric secretion in the lumen-perfused stomach preparation. Furthermore, GRP inhibited gastric secretion stimulated by pentagastrin or histamine dose-dependently, but not by carbachol. Simultaneous infusion of GRP and a beta adrenergic blocking agent, propranolol, an inhibitor of somatostatin release, did not alter the inhibitory effect of GRP on pentagastrin-stimulated gastric secretion. These results suggest that the inhibitory effect of GRP on gastric secretion in a stimulated condition is mediated via peptide hormones coreleased by GRP, and not via beta-adrenergic pathways.