Effect of isoprenaline on pentagastrin-stimulated gastric acid secretion in dogs with gastric fistula

Effect of nervous excitation on acid secretion in horses

Nervous excitation was induced by various means in horses provided with a gastric cannula. Insulin hypoglycaemia profoundly inhibited the basal acid output and volume secreted from the stomach. No clear effect on acid secretion was noted after administration of bethanechol, as the acid output was covered by the copious secretion of saliva. Atropine almost abolished the basal acid output. Sensoric stimulation by teasing caused a slight but not significant increase in the total acid output. These data suggest that cholinergic excitation might play a role in the stimulation of both volume and acid secretion in the horse. The inhibitory effect seen on these two parameters after insulin hypoglycaemia may hypothetically be ascribed to inhibitory impulses carried in peptide neurones of the vagal nerves or to inhibitory impulses in adrenergic nerves acting directly or indirectly on the parietal cells.

Dissociation of gastric acid and pepsinogen secretion in response to mercaptomethylimidazole--a new secretory compound

Mercaptomethylimidazole (MMI), a potent antithyroid drug of the thionamide group, induces both acid and pepsinogen secretion independently in control and pylorus ligated mice. The effect is dose dependent and the drug is more effective than histamine, carbachol or isoproterenol when administered by an intraperitoneal route. MMI-stimulated pepsinogen secretion could be dissociated from the acid secretion by the use of cimetidine and omeprazole which effectively block the acid secretion without affecting the pepsinogen output. Neither acid nor pepsinogen secretion by MMI is inhibited by atropine indicating a lack of muscarinic receptor involvement in both of the processes. Nifedipine and verapamil, the calcium antagonists, by inhibiting the MMI-induced acid secretion can also dissociate pepsinogen secretion from the acid secretion. Clonidine, an alpha 2-agonist, and hexobarbital, a membrane active barbiturate, also inhibit acid secretion without affecting the pepsinogen output. These data indicate that MMI induces pepsinogen secretion independent of acid secretion. Furthermore, MMI-stimulated acid secretion is not additive with that of the histamine indicating same site (H2-receptor) of action while its synergistic effect in presence of carbachol (muscarinic receptor) indicates different site of interaction of the two compounds. On the other hand, an additive effect of MMI and carbachol on pepsinogen secretion indicates that while the carbachol effect is mediated through the muscarinic receptor, MMI stimulates pepsinogen secretion through some still unknown mechanism.

Effect of terbutaline, a beta 2-adrenoreceptor agonist, on gastric acid secretion and serum gastrin concentrations in humans

Because beta-adrenoreceptor agonists inhibit gastrin-stimulated gastric acid secretion in animals, we postulated that the beta 2-adrenoreceptor agonist, terbutaline, would inhibit pentagastrin-stimulated acid secretion in humans. Moreover, we hypothesized that terbutaline might inhibit food-stimulated acid secretion, as gastrin is a major mediator of food-stimulated acid secretion. Subcutaneous terbutaline (0.25 mg) reduced acid secretion during intravenous infusion of a submaximal dose of pentagastrin by 30%-40% (p less than 0.005), even though terbutaline increased serum gastrin levels (p less than 0.05). Furthermore, subcutaneous (0.25 mg) or oral (5 mg) terbutaline, given before a homogenized steak meal was infused into the stomach, lowered mean food-stimulated acid secretion rates, despite enhanced postprandial serum gastrin concentrations. Terbutaline also increased serum gastrin concentrations in patients with Zollinger-Ellison syndrome and in vagotomized individuals. Thus, beta 2-adrenoreceptor agonists enhance gastrin release while at the same time inhibiting gastrin-stimulated acid secretion in humans.

Inhibitory effect of isoprenaline on gastric acid secretion in the rat. The role of endogenous histamine

In dogs beta-adrenoreceptor agonists inhibit gastric acid secretion stimulated by exogenous gastrin to a much greater extent than acid secretion stimulated by exogenous histamine. One possible explanation for this observation is that endogenous histamine is important in gastrin-mediated acid secretion and that isoprenaline and related beta-adrenoreceptor agonists block gastric mucosal histamine release. This possibility was tested in the present study in gastric lumen-perfused anaesthetized rats. Intravenous infusion of isoprenaline (12 microgram kg-1 h-1) inhibited maximal, pentagastrin-stimulated acid output by 50-70% (P less than 0.01), but had no significant inhibitory effect on the maximal acid secretory response to histamine. In contrast to its inhibitory effect on gastrin-stimulated acid output, isoproterenol had no effect on gastric histamine output during pentagastrin infusion. We conclude that isoprenaline selectively inhibits gastrin-stimulated acid secretion in the rat, as in the dog, and by a mechanism other than inhibiting gastric histamine release.

Effect of serotonin on bethanechol-stimulated gastric acid secretion and gastric antral motility in dogs

The purpose of the present study was to evaluate the effect of serotonin on bethanechol-stimulated gastric acid secretion and antral motility in conscious dogs with gastric fistula. Bethanechol stimulated the acid secretion dose-dependently and maintained the frequency and strength of the antral contractions at a high level. Serotonin inhibited the acid secretion dose-dependently, whereas the antral motility was stimulated. The acid inhibition was blocked by propranolol, and dose-response analysis showed inhibition of a non-competitive type. This study thereby shows that serotonin inhibits bethanechol-stimulated gastric acid secretion similarly to salmefamol (beta 2-adrenergic agonist)--that is, dose-dependently and non-competitively. Serotonin has been proposed to be a mediator of the beta-adrenergic influence on gastric function in vivo, but the counteracting effect of propranolol and the stimulatory effect of serotonin on motility contradict this hypothesis.

Beta-adrenergic agonists inhibit gastric acid and pepsin secretion through somatostatin release in dogs

The purpose of the present study was to evaluate whether the inhibitory effects of beta-adrenergic agonists on gastric secretory activity in vivo could be mediated through a local release of somatostatin. The gastric secretion was measured during continuous stimulation with pentagastrin (1 microgram/kg/h). The infusion of isoprenaline (beta 1 + beta 2), salmefamol (beta 2), and somatostatin produced inhibitory effects on both acid and pepsin secretion. The reaction patterns were similar for isoprenaline and somatostatin, whereas salmefamol induced an inhibition of longer duration and with dissimilar dose-response kinetics. The gastric somatostatin release was significantly increased after infusion of both beta-adrenergic agonists and somatostatin, with patterns similar to those obtained for the secretory inhibition. There was a significant correlation between the somatostatin release and the acid and pepsin secretion during infusion of the secretory inhibitors but not in the control state. This study shows that beta-adrenergic agonists have inhibitory effects on gastric secretion in vivo similar to those of somatostatin. Both somatostatin and the beta-adrenergic agonists stimulated the release of somatostatin from the gastric mucosa. beta-Adrenergic antagonists were without effects. Somatostatin thereby fulfils the requirements for an endogenous mediator of the beta-adrenergic inhibition.

Influence of beta blockade on gastric acid secretion and changes in gastric mucosal blood flow before and after parietal cell vagotomy in dogs and man

The aim of the present study was, in paired experiments in dogs, to examine the effect of beta-receptor blockade on gastric acid secretion and mucosal blood flow before and after parietal cell vagotomy (PCV). The secretory response to pentagastrin was reduced after vagotomy. beta-Adrenergic blockade had no effect on pentagastrin-stimulated gastric acid secretion before PCV, but after PCV beta blockade caused a modest increase in acid secretion, mediated mainly by the beta 2 receptors. A similar trend was seen in man. A marked increase in mucosal blood flow occurred 30 min after propranolol and was followed by a late decrease. One may conclude that a modest beta-adrenergic tone, which reduces secretion, becomes manifest after vagal denervation and that an increase in the ratio between mucosal blood flow and acid secretion was induced by the PCV. This increase cannot be explained as a beta-receptor-mediated effect.

Postvagotomy acid secretion and mucosal blood flow during beta-adrenoceptor stimulation and universal chemical sympathectomy in dogs

The aim of the present study was to examine the effect of beta-adrenoceptor stimulation, alpha blockade, and elimination of the adrenergic nerve function on mucosal blood flow and acid secretion in parietal-cell-vagotomized (PCV) gastric fistula dogs. Isoprenaline inhibited pentagastrin-stimulated gastric acid secretion via the beta 1 receptors non-competitively. The effect of isoprenaline was more pronounced after vagotomy than before vagotomy and significantly more pronounced than the effect on parasympathomimetically stimulated (bethanechol) gastric acid secretion. The animals were subjected to chemical sympathectomy with 6-hydroxy-dopamine, a false neurotransmitter that selectively destroys the adrenergic nerve terminals. Chemical sympathectomy increased the pentagastrin-stimulated gastric acid secretion and stabilized the mucosal blood flow at the level before vagotomy, but with an increased ratio between blood flow and acid secretion. One may conclude that the sympathetic nerve system influences gastric function after vagotomy.

Effect of isoprenaline on bethanechol-stimulated gastric antral motility in dogs with gastric fistula

The purpose of the present study was to evaluate the effect of isoprenaline on gastric antral motility in conscious dogs with gastric fistula, using intraluminal strain-gauge transducers. Infusion of bethanechol increased the motility for both frequency and strength. Isoprenaline, a beta 1- and beta 2-agonist, was used alone and in conjunction with selective blockade of beta 1 and beta 2 receptors. The stimulated antral motility was dose-dependently inhibited by isoprenaline. The effect was significantly blocked by the beta 1 + beta 2-adrenoceptor blocker propranolol and by using in conjunction the beta 1-adrenoceptor blocker practolol and the beta 2-adrenoceptor blocker H 35/25. H 35/25 and particularly practolol reduced the effect of isoprenaline to some extent, but the reduction was not of statistical significance. This indicates that isoprenaline acts on antral motility through both beta 2 and beta 1 receptors. Dose-response experiments with five logarithmically increasing doses of bethanechol and one dose of isoprenaline showed inhibition of a non-competitive type.

Effect of isoprenaline on bethanechol-stimulated gastric acid secrtion and mucosal blood flow in dogs with gastric fistula

The prupose of this study was to elucidate the effect of the beta-adrenoceptor stimulation by isoprenaline on cholinergic-stimulated gastric acid secretion and mucosal blood flow in conscious dogs with gastric fistula. Isoprenaline, a beta 1- and beta 2-agonist, was used alone and in conjunction with selective blockade of beta 2 and beta 1 receptors. A low dose of isoprenaline had no significant effect, whereas higher doses had a significant antisecretory effect. The antisecretory effect was significantly blocked by the beta 1-adrenoceptor blocker practolol but not by H 35/25, a beta 2-adrenoceptor blocker. The dose-response curve with five doses of bethanechol with and without isoprenaline was in accordance with a non-competitive inhibition. There was no significant effect on gastric mucosal blood flow, indicating that the acid inhibition was not secondary to changes in blood flow. The inhibitory effect of isoprenaline seems to be mediated by the beta 1 receptors and with an action primarily on the 'gastrinergic receptors'.

Effect of dopamine on pentagastrin-stimulated gastric acid secretion and mucosal blood flow in dogs with gastric fistula

The purpose of this study was to elucidate the effect of intravenously administered dopamine on dopamine receptors and adrenergic receptors in terms of its effect on gastric acid secretion, the kinetic mechanism, blood flow, and antral motility. Dopamine was used alone and in conjunction with selective blockade of alpha-, beta-, and dopaminergic receptors. A significant inhibition of gastric acid secretion was found with the highest dose of dopamine used (40 micrograms/kg/min). The kinetic study showed characteristics of a non-competitive type. The anti-secretory effect dopamine was significantly blocked by non-selective beta-blockade or by selective beta-blockade but not by alpha- or dopaminergic receptor blockade. This suggests that the inhibitory effect of dopamine on gastric secretion is mediated by beta-receptors. There was no significant effect on gastric mucosal blood flow, but the ratio between blood flow and acid secretion was significantly elevated during dopamine infusion, indicating that the acid inhibition was not secondary to changes in blood flow. It is concluded that the dopamine inhibition of acid secretion is mediated by beta 1-receptors, unlike the effect on antral gastric motility, which is mediated by dopamine receptors.

Effect of dopamine on pentagastrin-stimulated gastric antral motility in dogs with gastric fistula

The purpose of the present study was to evaluate the effect of dopamine on gastric antral motility in conscious dogs with gastric fistula by using miniature strain-gauge transducers. Infusion of pentagastrin changed the contractile activity to a digestive state. Dopamine, an endogenous catecholamine, was used alone and in conjunction with selective blockade or adrenergic and dopaminergic receptors. The stimulated antral motility was inhibited by dopamine. The effect was significantly blocked by the peripherally acting dopaminergic blocker domperidone and by cis-flupenthixol, which blocks both peripheral and central dopaminergic receptors. The effect of dopamine was not significantly altered by the beta 1-adrenoceptor blocker practolol, the alpha-adrenoceptor blocker phentolamine, or the alpha + beta-adrenoceptor blocker labetalol. Consequently, this study indicates that dopamine acts on gastric antral motility through dopaminergic receptors. beta-Adrenergic receptors, which are active in the impairment of gastric acid secretion, seem not to be involved in the motility response.

Effect of a beta 2-sympathomimetic on gastrin release, acid secretion, and blood glucose during basal conditions and in response to insulin, 2-deoxy-D-glucose, and feeding in the dog

The effect of a selective beta 2-adrenoceptor agonist on basal volume and on insulin-, 2-deoxy-D-glucose (2-DG)-, and food-induced gastrin release was studied in conscious gastric fistula dogs. Acid output and blood glucose changes were also studied, except in the food experiments. Basal acid secretion and serum gastrin were unchanged after beta 2-sympathetic infusion, whereas a slight increase in blood and glucose was found. The beta 2-agonist almost prevented acid output and gastrin release after insulin hypoglycaemia. However, the hypoglycaemia was also inhibited. Gastric acid secretion stimulated by 2-DG was inhibited, as was probably the gastrin release. 2-DG increased the blood glucose level, and no significant differences were found after beta 2 infusion. After feeding, gastrin release was initially decreased for one of five doses of the beta 2-agonist, and higher doses of the beta 2-agonist prevented the subsequent fall in serum gastrin after the initial peak value. This pattern was also found for the histamine H2-blocker cimetidine in a dose that blocks acid output. The beta 2-agonist and 2-DG increased pulse rate. It is concluded that beta 2-sympathetic stimulation inhibits acid output and gastrin release after insulin and 2-DG stimulation, but one should be cautions in drawing conclusions from the insulin experiments. The effect on gastrin release is small compared with the effect on the acid secretion, and it is unlikely that the inhibition of acid secretion acts through a change in gastrin release.

Release of prostaglandin E2 into gastric juice during stimulation of muscarinic- and gastrin receptors in dogs and in humans

To investigate the causal relationship, if any, between gastric PG formation and gastric acid output, the release of PGE2 into gastric juice has been studied in eight beagle dogs with a gastric fistula, using sustained half-maximal stimulation by bethanechol and pentagastrin, and in eight duodenal ulcer patients, using the combined sham feeding/pentagastrin test. Immunoreactive PGE2 was determined by a method validated by gas chromatography-mass spectrometry and PGE2 values were normalized by expressing them as ng PGE2 released per meq H+ secreted. In the dogs "steady state" PGE2 output (0.4-10 ng/meq H+) was interrupted during continuous i.v. pentagastrin infusion by symmetrical peaks (50-60 minutes of duration) with a maximum of 24 +/- 3.1 ng/meq H+ (mean +/- SEM). During bethanechol stimulation the rhythmic variations were smaller, but the median values for the periods 30 to 180 or 240 minutes significantly (p less than 0.01) higher (3.9-46 ng/meq H+) than in pentagastrin experiments (0.8-20 ng/meq H+). In humans the peak PGE2 output during sham feeding (3.4-41 ng/meq H+) was significantly (p less than 0.02) larger than following bolus stimulation (6/micrograms/kg) by pentagastrin (2.2-18 ng/Meq H+). The findings are consistent with the hypothesis that activation of muscarinic receptors represents the physiologic mechanism by which gastric release of PGs is regulated. Cyclic variations in gastric PG formation appear to occur in response to vagal stimulation since the peaks in PGE2 output were preceded by increased myoelectrical activity (i.e. mean contractile index).