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

Distribution of urocortin in the rat's gastrointestinal tract and its colocalization with tyrosine hydroxylase

Urocortin (Ucn), a newly identified member of the corticotropin-releasing factor (CRF) family, is not only expressed in the brain, but also abundantly present in the peripheral tissues, especially in the gastrointestinal tract (GI) as determined by radioimmuoassay. In order to determine the precise localization of urocorin in the GI, we mapped the distribution of urocortin-like immunoreactivity (ir) in the GI of the rat using an immunofluorescence histochemical technique. Ucn, both in the brain and the peripheral tissues, is involved in the regulatory control of host-defense mechanism during stress. In order to study the possible involvement of the sympathetic system in the expression of GI urocortin in response to stress, we examined the effect of chemical sympathectomy on urocortin-ir and its colocalization with tyrosine hydroxylase (TH). UCn was expressed in all parietal cells of the stomach, myenteric and submucosal plexuses as well as in cells in Lieberkühn crypts of the small and large intestine. Most of the acid secreting parietal cells contained both Ucn and TH. Chemical sympathectomy did not affect Ucn immunoreactivity of parietal cells.

Immunohistochemical study of dopamine in rat gastric mucosa with acute gastric ulcer

Recent studies have shown the presence of dopamine (DA) in gastric and duodenal mucosa, and changes in gastric mucosal DA content have been observed in patient with acute ulcers. Immunohistochemical demonstration of the distribution of DA in gastric mucosa under stress was studied by light and electron microscopy. In the control group, DA was present in the gastric gland proper in the gastric corpus and antrum on light microscopy, and on the surface of mucous granules in chief cells, mucous neck cells, and surface epithelium on electron microscopy. In the stress group, DA in gastric mucosa was almost undetectable on light and electron microscopy. Further, in this group serum DA concentration was significantly higher in the portal vein than in the abdominal aorta. Endogenous DA in gastric mucosal cells may affect gastric mucosa differently from exogenous DA, and stress may release endogenous intracellular DA into extracellular spaces.

Effect of dopamine on prostaglandin E2 content in gastric mucosa

The effects of dopamine (DA) on the prostaglandin (PG) E2 content of rat gastric mucosa was investigated. There was a 17.5% increase in gastric mucosal blood flow (BF) after administration of DA (5 micrograms/kg/min iv). After pretreatment with fusaric acid (FA), an antagonist of dopamine beta hydroxylase, DA increased BF by 27.8%. The PGE2 content in DA and DA + FA groups increased at rates of 45.8% and 42.4%, respectively. The PGE2 content in gastric mucosa after incubation following Basso's method, increased in the DA, DA + FA and noradrenaline (NA) groups to 3.32 +/- 0.40 micrograms/g, 3.30 +/- 0.39 micrograms/g and 3.37 +/- 0.42 micrograms/g respectively. It is concluded that there are no differences in PGE2 content among the DA, DA + FA and NA groups. The mechanism by which PGE2 content increases after administration of DA is the direct action of DA and/or increasing BF. It is suspected that DA directly affects PGE2 synthesis, however the possibility that DA is metabolized to NA, which secondarily results in increased PGE2 synthesis, cannot be excluded.

Cisapride offsets dopamine-induced slowing of fasting gastric emptying

The effect of cisapride, a new gastrokinetic drug, on gastroduodenal motility was tested in six healthy volunteers. In order to obtain a model for slowed gastric emptying, dopamine was infused at a rate of 8 micrograms/kg/min. Dopamine significantly slowed the fractional emptying rate of fasting gastric contents from 5.14 +/- 0.37 to 1.45 +/- 0.67 %/min. Injection of either 10 mg of cisapride or 10 mg of metoclopramide restored emptying rate to normal (5.87 +/- 0.56 and 5.62 +/- 0.61 %/min, respectively). When cisapride was given without dopamine background, emptying was only moderately enhanced. Reflux of bile salts was not significantly affected by either cisapride or dopamine alone. When given on a dopamine background, however, both metoclopramide and cisapride decreased bile salt reflux below control values without any active treatment. It is concluded that emptying of fasting gastric contents can be speeded by cisapride, particularly when emptying is slowed by dopamine. A clear effect on bile salt reflux cannot be demonstrated.

Somatostatin increases the ratio between gastric mucosal blood flow and gastric acid and pepsin secretion in dogs

The effects of somatostatin on gastric mucosal blood flow (GMBF), acid secretion, and pepsin secretion were evaluated. Conscious gastric fistula dogs were used, with neutral red clearance as the method for estimating the mucosal blood flow. Somatostatin inhibited the pentagastrin- and bethanechol-stimulated gastric acid and pepsin secretion and resulted in an absolute decrease in mucosal blood flow. The ratios between GMBF and secretion (acid and pepsin) were increased during somatostatin infusion, which suggests a relative increase in mucosal blood flow and independent inhibition of gastric secretion. It may be concluded from this study that the acid- and pepsin-inhibitory effects of somatostatin are not mediated by changes in the GMBF.

Lack of effect of domperidone on gastrin release: evidence for a peripheral activity of the drug

The effect of intravenous administration of domperidone, a dopamine receptor antagonist with peripheral activity, on basal and submaximal pentagastrin-stimulated gastric acid secretion and gastrin release has been evaluated in healthy volunteers. No significant changes were observed in the parameters studied. The lack of effect on gastrin release appears to confirm that domperidone is unable to penetrate the blood brain barrier in appreciable amounts in adults.

Dopaminergic control of gastric acid and gastrin secretion in man: lack of effects after acute oral administration of ibopamine, an analogue of dopamine

The effect of oral administration of the dopaminergic drug, ibopamine, at the dose of 200 mg and 400 mg, on basal and submaximal pentagastrin (0.25 microgram kg-1 h-1) stimulated gastric acid secretion as well as basal serum gastrin concentration has been evaluated in 24 healthy individuals. In comparison with placebo no significant changes were observed in all the variables studied. The lack of effects on gastric acid secretion might be due to a selective stimulation of dopaminergic receptors not active in the regulation of gastric acidity or not present in gastric mucosa, while unchanged serum gastrin secretion is possibly due to a poor crossing of blood-brain barrier by ibopamine.

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.

The effect of alpha- and beta-adrenergic agonists and blockers on postprandial pancreatic polypeptide release in dogs

The influence of adrenergic agonists--phenylephrine (alpha), isoproterenol (beta), and salbutamol (beta 2)--and of adrenergic blockers--phentolamine (alpha), pranolol (beta), and practolol (beta 1)--on the postprandial pancreatic polypeptide (PP) release has been assessed in five Labrador retrievers. Infusions of phenylephrine, 0.12 mg kg-1h-1; isoproterenol, 3 micrograms kg-1h-1; salbutamol, 12 micrograms kg-1h-1, did not significantly affect PP release. Propranolol, 0.5 mg kg-1, and propranolol, 0.5 mg kg-1, + phentolamine, 1 mg kg-1, combined, given as intravenous boluses before the meal significantly reduce PP release (44% and 58% of controls, p less than 0.05), whereas phentolamine, 1 mg kg-1, and practolol, 1 mg kg-1, had no effect. Phenylephrine combined with phentolamine and isoproterenol combined with propranolol and practolol did not influence PP secretion. It is concluded that the postprandial PP release is stimulated by beta 2-adrenergic mechanisms.

Effect of dopamine on bethanechol-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, using intraluminal strain-gauge transducers. Infusion of bethanechol increased the motility with regard to both frequency and strength. Dopamine, an endogenous catecholamine, was used alone and in conjunction with selective blockade of adrenergic and dopaminergic receptors. The stimulated antral motility was dose-dependently inhibited by dopamine. The effect was significantly blocked by the peripherally acting dopaminergic blocker domperidone. The alpha-adrenoceptor blocker phentolamine reduced the effect of dopamine to some extent, but the reduction was not of statistical significance. The dopamine-inhibited motility was not altered by the beta 1-adrenoceptor blocker practolol or the beta 1 + beta 2-adrenoceptor blocker propranolol. This indicates that dopamine acts on gastric antral motility predominantly through dopaminergic receptors. beta-Adrenergic receptors, which are active in the impairment of gastric acid secretion, do not seem to be involved in the motility response. Dose-response investigations with five increasing doses of bethanechol and one dose of dopamine 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 bethanechol-stimulated gastric mucosal blood flow and gastric acid secretion in dogs with gastric fistula

The aim of the present study was to investigate the effect of Dopamine on bethanechol-stimulated gastric acid secretion and mucosal blood flow. dopamine was used alone and in conjunction with selective blockade of the alpha, beta, and dopaminergic receptors. An increasing and dose-dependent stimulation of gastric acid secretion was found for dopamine at 1, 5, and 10 micrograms/kg/min. A significant inhibition of gastric acid secretion was found with the highest dose of dopamine (40 micrograms/kg/min). the stimulatory effect seems to be mediated by more than one receptor, whereas the inhibition by high dopamine doses could be explained by a beta 1 stimulation. Dopamine (10 micrograms/kg/min) was found to increase the bethanechol-stimulated gastric mucosal blood flow. Phentolamine (alpha blackade) increased this dopamine-elevated blood flow further, with a significant increase in the ratio between blood flow and acid secretion, indicating a primary action of the alpha receptors on blood flow. Bethanechol stimulated the gastric acid secretion and blood flow in a parallel manner. It is concluded that alpha-receptor stimulation is the predominant directly acting factor in the regulation of gastric mucosal blood flow, whereas stimulation of beta, muscarinic, and 'gastrinergic' receptors mainly occurs indirectly via changes in parietal cell function. The main effect of dopamine seems to be on gastric motility, whereas the effect on gastric acid secretion is of minor importance.

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.