Effects of dopamine agonists and antagonists on gastric acid secretion and stress responses in rats

From Selye's and Szabo's Cysteamine-Duodenal Ulcer in Rats to Dopamine in the Stomach: Therapy Significance and Possibilities

We reviewed gastric ulcer healing by dopamine considering several distinctive duodenal key points. Selye and Szabo describe the cysteamine-induced duodenal ulcer in rats as a duodenal stress ulcer in patients. Szabo's cysteamine duodenal ulcer as the dopamine duodenal healing and cysteamine as a dopamine antagonist signifies the dopamine agonists anti-ulcer effect and dopamine antagonists ulcerogenic effect. From these viewpoints, we focused on dopamine and gastric ulcer healing. We mentioned antecedent studies on the dopamine presence in the stomach and gastric juice. Then we reviewed, in the timeline, therapy significance arising from the anti-ulcer potency of the various dopamine agonists, which is highly prevailing over the quite persistent beneficial evidence arising from the various dopamine antagonists. Meanwhile, the beneficial effects of several peptides (i.e., amylin, cholecystokinin, leptin, and stable gastric pentadecapeptide BPC 157, suggested as an acting mediator of the dopamine brain-gut axis) were included in the dopamine gastric ulcer story. We attempt to resolve dopamine agonists/antagonists issue with the dopamine significance in the stress (cysteamine as a prototype of the duodenal stress ulcer), and cytoprotection (cysteamine in small dose as a prototype of the cytoprotective agents; cysteamine duodenal ulcer in gastrectomized rats). Thereby, along with dopamine agonists' beneficial effects, in special circumstances, dopamine antagonists having their own ulcerogenic effect may act as "mild stress (or)" or "small irritant" counteracting subsequent strong alcohol or stress procedure-induced severe lesions in this particular tissue. Finally, in the conclusion, as a new improvement in further therapy, we emphasized the advantages of the dopamine agents' application in lower gastrointestinal tract therapy.

Activation of dopamine D2 receptor promotes pepsinogen secretion by suppressing somatostatin release from the mouse gastric mucosa

In vivo administration of dopamine (DA) receptor (DR)-related drugs modulate gastric pepsinogen secretion. However, DRs on gastric pepsinogen-secreting chief cells and DA D2 receptor (D2R) on somatostatin-secreting D cells were subsequently acquired. In this study, we aimed to further investigate the local effect of DA on gastric pepsinogen secretion through DRs expressed on chief cells or potential D2Rs expressed on D cells. To elucidate the modulation of DRs in gastric pepsinogen secretion, immunofluorescence staining, ex vivo incubation of gastric mucosa isolated from normal and D2R-/- mice were conducted, accompanied by measurements of pepsinogen or somatostatin levels using biochemical assays or enzyme-linked immunosorbent assays. D1R, D2R, and D5R-immunoreactivity (IR) were observed on chief cells in mouse gastric mucosa. D2R-IR was widely distributed on D cells from the corpus to the antrum. Ex vivo incubation results showed that DA and the D1-like receptor agonist SKF38393 increased pepsinogen secretion, which was blocked by the D1-like receptor antagonist SCH23390. However, D2-like receptor agonist quinpirole also significantly increased pepsinogen secretion, and D2-like receptor antagonist sulpiride blocked the promotion of DA. Besides, D2-like receptors exerted an inhibitory effect on somatostatin secretion, in contrast to their effect on pepsinogen secretion. Furthermore, D2R-/- mice showed much lower basal pepsinogen secretion but significantly increased somatostatin release and an increased number of D cells in gastric mucosa. Only SKF38393, not quinpirole, increased pepsinogen secretion in D2R-/- mice. DA promotes gastric pepsinogen secretion directly through D1-like receptors on chief cells and indirectly through D2R-mediated suppression of somatostatin release.

Multicomponent, multitarget integrated adjustment - Metabolomics study of Qizhiweitong particles curing gastrointestinal motility disorders in mice induced by atropine

ETHNOPHARMACOLOGICAL RELEVANCE

Qizhiweitong particles (QZWT) which is derived from the Sinisan decoction in Shang Han Za Bing Lun, composed of Bupleurum chinenis, Paeonia obovata, Citrus aurantium L., Glycyrrhiza uralensis Fisch., Cyperus rotundus and Rhizoma Corydalis is a traditional Chinese medicine (TCM) treating gastrointestinal diseases. It have been used in clinical for years. It have been used in clinical for years. According to previous research, Bupleurum chinenis, Citrus aurantium, Cyperus rotundus in QZWT play the role of promoting gastric peristalsis, which consist of complex chemical constituents. The aim of this study is to probe the multiple effective components with gastrointestinal prokinetic efficacy in QZWT and investigate the multitarget integrated adjustment mechanism of QZWT curing atropine-induced gastrointestinal motility dysfunction mice.

MATERIALS AND METHODS

One hundred and thirty two male mice were randomly divided into 11 groups, including control group, model group, Domperidone group, Mosapride group, QZWT group and six components groups. With gastric retention rate, rate of small intestine propulsion, serum content of GAS and MTL as indexes to evaluate the curing effect on gastrointestinal movement disorders caused by atropine in mice. A serum metabonomics method based on the ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) had been established to investigate the mechanism of QZWT and these components, and PCA and PLS-DA have been used to distinguish different groups and found potential biomarkers.

RESULTS

Four components from six present good prokinetic effects, including Bupleurum Polysaccharide, Citrus aurantium flavonoid, Citrus aurantium essential oil and Cyperus rotundus flavonoids. These components and QZWT regulate 5 potential biomarkers in the body, and primarily involved in 5 metabolic pathways. These potential biomarkers possess direct or indirect connections, each biomarker regulated by multiple components, each component adjusting multiple targets, and QZWT is nearly the sum of its components.

CONCLUSIONS

This experiment deepened our understanding of insufficient gastrointestinal dynamics, confirmed that QZWT treating gastrointestinal disorders was through multicomponent, multitarget ways. These results fully reflect the multiple targets synergy characteristics of TCM.

A comparison of the effects of gastrin, somatostatin and dopamine receptor ligands on rat gastric enterochromaffin-like cell secretion and proliferation

Gastrin regulates ECL cell histamine release and is a critical determinant of acid secretion. ECL cell secretion and proliferation is inhibited by gastrin antagonists and somatostatin but little is known about the role of dopamine agonists in this process. Since the ECL cell exhibits all three classes of receptor we evaluated and compared the effects of the gastrin receptor antagonist, (YF476), lanreotide (SST agonist) and novel dopaminergic agents (BIM53061 and BIM27A760) on ECL cell histamine secretion and proliferation. Highly enriched (>98%) ECL cell preparations prepared from rat gastric mucosa using a FACS approach were studied. Real-time PCR confirmed presence of the CCK2, SS2 and SS5 and D1 receptors on ECL cells. YF476 inhibited histamine secretion and proliferation with IC(50)s of 1.25 nM and 1.3 x 10(-11) M respectively, values 10-1000x more potent than L365,260. Lanreotide inhibited secretion and proliferation (2.2 nM, 1.9 x 10(-10) M) and increased YF476-inhibited proliferation a further 5-fold. The dopamine agonist, BIM53061, inhibited gastrin-mediated ECL cell secretion and proliferation (17 nM, 6 x 10(-10) M) as did the novel dopamine/somatostatin chimera BIM23A760 (22 nM, 4.9 x 10(-10) M). Our studies demonstrate that the gastrin receptor antagonist, YF476, is the most potent inhibitor of ECL cell histamine secretion and proliferation. Lanreotide, a dopamine agonist and a dopamine/somatostatin chimera inhibited ECL cell function but were 10-1000x less potent than YF476. Agents that selectively target the CCK2 receptor may provide alternative therapeutic strategies for gastrin-mediated gastrointestinal cell secretion and proliferation such as evident in the hypergastrinemic gastric carcinoids associated with low acid states.

Methylphenidate blood levels and therapeutic response in children with attention-deficit hyperactivity disorder: I. Effects of different dosing regimens

BACKGROUND AND PURPOSE

Methylphenidate (MPH) is a drug of choice for treating attention-deficit/hyperactivity disorder (ADHD), although its use has been complicated by its short duration of action. The development of ideal long-acting preparations requires detailed understanding of the pharmacokinetic and pharmacodynamic consequences of complex dosing regimens. The purpose of this study was to ascertain if administration paradigms that produce stable or rising MPH levels alter the rate with which MPH is absorbed, and to determine how effectively long-acting administration paradigms compare with thrice daily administration of immediate-release MPH.

METHOD

Forty-eight boys diagnosed with ADHD (mean age 10.6 +/- 1.1 year) participated in this double-blind, parallel group study to evaluate the pharmacokinetics and efficacy and of 1 mg/kg/day MPH administered in five different paradigms and placebo. Objective measures of activity and attention (McLean Motion Attention Test; M-MAT) and plasma measures of d- and l-MPH were obtained hourly during the course of a 12-hour laboratory session.

RESULTS

The rate of absorption and elimination of d-MPH was dependent on the pattern of administration, particularly on the initial bolus concentration. This suggests that d-MPH may act on the gastrointestinal system to slow absorption of additional d-MPH. There were significant differences among regimens on time course and degree of therapeutic response. Pulsatile administration produced greater improvement than escalating levels.

Susceptibility of dopamine D5 receptor targeted mice to cysteamine

BACKGROUND

Recently we demonstrated that gastric mucosa of rats can synthesize, store and release dopamine. Out of five different subtypes, mRNA of D5 (=D1b) dopamine receptor is very abundant in the gastric epithelium. D1 receptor selective dopamine agonists have been shown to protect against experimental gastro-duodenal lesions.

AIMS

To test the hypothesis that protective effects of dopamine involve D5 receptors, mucosal lesions were induced in D5 receptor deficient (KO) and wild-type (WT) mice using cysteamine. Morphology and gastric acid secretion of D5 KO mice were also studied.

METHODS

Single doses of 600 mg/kg, 300 mg/kg cysteamine or vehicle were administered subcutaneously to fasted animals. After 24 h, number and severity of gastro-duodenal lesions were analyzed. Basal and histamine-induced maximal gastric acid output were measured by a stomach-sac wash-through method.

RESULTS

All the KOs in the 600 mg/kg cysteamine group died within 4 h showing symptoms of toxicity while three out of four WTs survived (P<0.05). Mortality after 300 mg/kg cysteamine was significantly higher in KOs versus the WTs: 6/14 versus 2/11, P<0.05. Gastric lesion-index was also significantly higher in KOs (median, middle quartile): four (3-9) versus 0 (0-0), P<0.05. Duodenal lesions did not develop from this single dose of cysteamine in either genotype. Basal and histamine-induced maximal gastric acid output were comparable in the two genotypes.

CONCLUSIONS

This study demonstrates that loss of D5 receptor causes mucosal vulnerability and increased toxicity of cysteamine in genetically manipulated mice. Thus, D5 receptor subtype is indeed likely to be involved in protective effects of dopamine in the stomach.

Dopamine produced by the stomach may act as a paracrine/autocrine hormone in the rat

Dopamine (DA) has been suggested to be a protective factor in the gastrointestinal tract but neither a source of DA nor its exact targets of action have been identified. In this study, we demonstrate high levels of DA (and DOPA) which persist after chemical sympathectomy in the gastric juice of rats. Immunostaining and in situ hybridization histochemistry reveal the presence of tyrosine hydroxylase (TH), DA transporter and vesicular monamine transporters in the acid-producing parietal cells. Like DA, TH enzyme activity remains after chemical sympathectomy. We also demonstrate active reuptake and storage of DA that indicates a regulated release of this neurohormone from parietal cells. DA D1b receptor mRNA is the most abundant DA receptor subtype in gastric and duodenal epithelium. Therefore, we suggest that selective DA D1b receptor agonists may be useful adjuncts in the treatment of duodenal and gastric ulcers. Gastric epithelia possess the hallmarks of functional DA neuroendocrine cells, suggesting that DA has an important role in self-protective mechanisms of the gastrointestinal tract. These findings should allow elucidation of DA role in normal and disease states in the stomach and duodenum.

Dopaminergic characteristics of isolated parietal cells from rats

Recently we have identified a dopamine-producing system in the gastric mucosa of rats. All the available morphological data suggest that parietal cells synthesize dopamine. In the present study we investigated the dopaminergic characteristics of isolated parietal cells by different methods. Mixed gastric mucosal cells were isolated and size-fractionated by elutriation. The proportion of neurons, parietal and endocrine cells in the fractions were determined by immunocytochemistry (ICC) using antibodies to neurofilament, proton pump and chromogranin A, respectively. No neurons were found in any of the cell preparations, while 56% parietal cell and 0.0% endocrine cell were achieved in the parietally enriched fraction. By Western blot, a tyrosine hydroxylase (TH, the rate-limiting enzyme of the catecholamine synthesis) immunoreactive protein species was demonstrated in isolated mucosal cells, comigrating with the TH immunoreactivity from PC12 cells. The TH immunoreactivity was colocalized to parietal cells by ICC. Dopamine transporter (DAT), a regulator of extracellular/intracellular dopamine balance in the nervous system, was also demonstrated in parietal cells. A significant amount of dopamine and DOPA were measured by HPLC (13.4 and 9.57 pg/10(6) cell, respectively) in parietally enriched cell fraction. Since this enriched cell fraction was virtually clear of both neurons and endocrine cells, demonstration of TH enzyme, DAT and dopamine in this fraction confirms that the parietal cell population might be a major source of dopamine in the rat stomach, supporting our previous results achieved using whole tissue samples.

Dopamine and the regulation of cell proliferation in gerbil (Meriones unguiculatus) pyloric mucosa

The epithelium of the digestive system mucosa consists of a highly dynamic cell population. The conditions under which mitotic activity in the gastrointestinal epithelium is regulated is as yet poorly understood. Nevertheless, it is assumed that some biogenic amines might be involved. Having demonstrated that dopaminergic cells occur in the stomach of gerbils (Meriones unguiculatus), in the present study we examined the influence of dopamine antagonist haloperidol on the proliferation of epithelial cells in the mucosa of the stomach. Proliferating cells were detected immunocytochemically and quantified after in-vivo labeling with 5-bromo-2'-desoxyuridine in both haloperidol- and saline-treated animals. The results show that acute doses of haloperidol significantly increases the proliferation rate in the pyloric mucosa, suggesting that dopamine plays a probable modulatory role in the regulation of mitotic activity. These findings are discussed with regard to the role of paraneurons in regulating epithelial mitosis.

A novel nonneuronal catecholaminergic system: exocrine pancreas synthesizes and releases dopamine

Cells of the exocrine pancreas produce digestive enzymes potentially harmful to the intestinal mucosa. Dopamine has been reported to protect against mucosal injury. In looking for the source of dopamine in the small intestine, we found that the duodenal juice contains high levels of dopamine and that the pancreas itself has a high dopamine [and dihydroxyphenylalanine (dopa)] content that does not change significantly after chemical sympathectomy. Furthermore, we were able to demonstrate tyrosine hydroxylase (TH) activity in control pancreas as well as in pancreas from rats after chemical sympathectomy. Immunostaining and in situ hybridization histochemistry confirmed both the presence of TH, dopamine, and the dopamine transporter, and the mRNAs encoding TH and dopamine transporter, and the presence of both types of vesicular monoamine transporters in the exocrine cells of the pancreas. Since there are no catecholaminergic enteric ganglia in the pancreas, the above results indicate that pancreatic cells have all the characteristics of dopamine-producing cells. We suggest that the pancreas is an important source of nonneuronal dopamine in the body, and that this dopamine has a role in protecting the intestinal mucosa and suggests that dopamine D1b receptor agonists might be used to help mucosal healing in the gastrointestinal tract.

Gastric and duodenal anti-ulcer activity of SKF 38393, a dopamine D1-receptor agonist in rats

The effect of SKF 38393 (1-phenyl-7,8-diol-2,3,4,5-tetrahydro-1H-3-benzazepine), a specific dopamine D1-receptor agonist, was studied on pylorus-ligation and water immersion plus restraint stress-induced gastric ulcers, and cysteamine-induced duodenal ulcers in rats. Repeated administration of SKF 38393 (5 and 10 mg kg-1, p.o.) for six days was found to be effective in the prevention of gastric ulceration induced by water immersion plus restraint stress in rats. In 19-h pylorus-ligated rats, repeated treatment with SKF 38393 showed a significant reduction in the number and severity of ulcers. SKF 38393 did not alter the total gastric-mucosal carbohydrates:protein ratio; however, the gastric content volume and the free and total acidity were significantly reduced. In cysteamine-induced duodenal ulcers, the treatment with SKF 38393 for 6 days prevented the duodenal lesions. Our data suggests the involvement of dopamine D1 receptors in the anti-ulcer activity of SKF 38393, which could be largely attributed to its anti-secretory effect. Its anti-ulcer activity against water immersion plus restraint, also points towards a central mode of action, but its failure to alter the carbohydrate:protein ratio rules out any protective effect through the strengthening of the gastric mucosal barrier.

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.

Restraint stress in biomedical research: an update

Since the publication of our initial review of restraint stress in 1986, much work has continued with this technique, either as a tool for the investigation of other pharmacological, physiological, or pathologic phenomena or with restraint stress itself serving as the object of the study. As we noted in 1986, the major use of restraint has been for the induction of stress responses in animals and, more specifically, for the investigation of drug effects, particularly as they affect typical stress-related pathology--gastrointestinal, neuroendocrine, and immunological agents have been extensively studied. In compiling this update on restraint stress and its effects, we noted an increasing emphasis on central nervous system mechanisms in peripheral disease, especially gastrointestinal disease. In particular, many CNS-active agents have been tested for their effects on gastric and duodenal lesion formation and gastric secretion, including antidepressants, antipsychotics, anxiolytics, noradrenergic, serotonergic, dopaminergic, and peptidergic compounds. Some of these agents are especially active in the gastrointestinal tract even when administered centrally, further solidifying the concept of a brain-gut axis. The present update includes studies of: methods and procedures, pre-restraint manipulations, post-restraint/healing effects, and drug effects. In addition, a current bibliography of reports that have employed restraint is included.

Central nervous system and gut interactions: dopamine and experimental gastroduodenal lesions

There is increasing evidence for brain regulation of gastroduodenal function and pathological responses. This laboratory has demonstrated a significant role for dopamine (DA) as a modulator of gastrointestinal function and disease. Using models of both acute (ethanol restraint stress; cysteamine) and chronic (iodoacetamide-induced gastritis) gastroduodenal mucosal injury, as well as tests of gastric secretory function (conscious basal gastric acid secretion; pylorus ligation; ex vivo gastric chamber), we have shown that DA, particularly DA1/D1 receptor agonists are powerful gastroprotective agents. This action is demonstrable upon peripheral administration as well as central (particularly intramesolimbic) administration. DA1/D1 agonists such as SKF38393 and SKF75670C reduce experimental gastric mucosal injury and secretion while antagonists of these receptors, including SCH23390, worsen experimental gastroduodenal lesions and augment secretion. That there exists a significant central component to DA-induced gastroprotection is demonstrated by data showing that rats assessed as anxiety prone, develop a greater degree of experimentally induced gastric damage, require greater amounts of DA agonists for 50% gastroprotection and respond to exogenous stress challenge with greater central DA turnover and loss, relative to rats assessed as low in anxiety. Very recently, we showed that dopamine D4 receptor blockade by clozapine and activation of dopamine D3 receptors by 7-hydroxy-N, N-di-n-propyl-2-aminotetralin (7-OHDPAT) are also associated with antiscretory and gastroprotective effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Clozapine, a dopamine DA4 receptor antagonist, reduces gastric acid secretion and stress-induced gastric mucosal injury

Dopamine and its agonists modulate a variety of gastrointestinal functions. In light of the increasing attention directed toward novel dopamine receptors and compounds that are active at these sites, we examined the effects of a dopamine D4 antagonist and putative antipsychotic, clozapine, in a model of conscious basal gastric acid secretion and in a model of stress-induced gastric mucosal injury. At a dose of 10.0 mg/kg i.p., clozapine significantly inhibited basal gastric acid secretion by 84% relative to vehicle. Lower doses (2.5 and 5.0 mg/kg) were inactive. Doses of 2.5, 5.0 and 7.5 mg/kg i.p. all significantly reduced restraint stress-induced gastric mucosal injury in rats. The highest dose inhibited gastric lesions by 70% relative to vehicle. We conclude that dopamine D4 receptors, present in high concentrations in mesolimbic brain regions, modulate gastric function and pathology in addition to mesolimbic D1 receptors, whose role in gastrointestinal function is already established.

Dopamine antagonists act on central, but not peripheral, receptors to inhibit sham and real feeding

We examined the relative contribution of dopamine (DA) receptors in the brain and periphery in the control of sham and real feeding of sucrose solutions. Intraperitoneal (IP) administration of pimozide, an antagonist of peripheral and brain DA receptors, suppressed both sham and real feeding in a dose-related manner. In contrast, IP injections of domperidone, a DA antagonist restricted to peripheral receptors, had no effect on either sham or real feeding. The inability of domperidone to influence sucrose intake did not result from a lack of biological activity of the drug because the identical doses of domperidone that failed to alter eating significantly inhibited gastric acid secretion. The results implicate central, but not peripheral, DA receptors in the control of the ingestion of palatable foods and also suggest that sham feeding is more sensitive to DA antagonism than real feeding.

Dopamine: a stress modulator in the brain and gut

1. Central dopamine (DA) exhibits large and rapid responses to stress challenge, particularly in the mesolimbic DA tract and, to a lesser degree, in the mesocortical tract. 2. Over the last few years, there has emerged an increasing role for peripheral DA, especially gastrointestinal DA, as a modulator of gastroduodenal injury consequent to stress exposure. 3. Evidence has accumulated which strongly supports a role for DA as an endogenous gastroprotective element and it appears that the dopaminergic "brain-gut axis" is a critical determinant of gastroduodenal mucosal integrity in the stress-challenged gut.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.

Dopamine in gastrointestinal disease

Dopamine is an important enteric neuromodulator. Herein we review the data that support a role for dopaminergic involvement in experimental duodenal and gastric ulceration; gastric, pancreatic, and duodenal secretion; gastrointestinal motility; and gastric and intestinal submucosal blood flow regulation. There also is support for a role for dopamine and dopamimetic agents in the treatment of certain experimental gastrointestinal diseases because some highly selective dopamine agonists are gastroprotective when given either parenterally or centrally. Based upon these observations, we suggest that dopamine is a key element of the "brain-gut axis" and represents a potentially important target for pharmacotherapeutic exploitation.

Effects of restraint stress on catecholamine concentrations in the glandular stomach of rats

Restraint stress is known to induce gastric ulcers in rats. Peripheral sympathetic activity and catecholamines are involved in the pathogenesis of these gastric ulcers. The aim of the present study was to evaluate the effects of restraint on mucosal and muscle catecholamine concentrations in the glandular stomach of rats. In unrestrained rats, noradrenaline concentration was higher in the muscle than in the mucosa of the glandular stomach (629 +/- 106 vs 18 +/- 3 pg/mg and 217 +/- 37 vs 18 +/- 8 pg/mg, respectively in the corpus and the antrum, p less than 0.01). This can be explained by the existence of an abundant noradrenergic innervation in the muscle layer. After 20 hours of restraint, adrenaline and noradrenaline concentrations were significantly decreased in adrenals, in comparison with unrestrained animals (255 +/- 53 vs 638 +/- 160 ng/mg and 113 +/- 17 vs 198 +/- 37 ng/mg, respectively for adrenaline and noradrenaline, p less than 0.05). In the glandular stomach, noradrenaline and adrenaline concentrations in restrained rats were not significantly different from those in unrestrained rats. However, adrenaline concentrations in the muscle of restrained rats were higher than in the mucosa. Moreover, restraint induced a significant decrease in dopamine concentration in the antral mucosa (from 100 +/- 12 pg/mg in unrestrained rats to 15 +/- 5 pg/mg in restrained rats), suggesting that a depletion in dopamine in the antral mucosa could be one of the pathogenetic factors involved in antral gastric stress-induced ulcers in rats.

Monoamine oxidase B inhibition reduces gastric mucosal blood flow, basal acid secretion, and cold water restraint-induced gastric mucosal injury in rats

Inhibition of monoamine oxidase B (MAO B) by selective inhibitors pargyline and L-deprenyl increases dopamine (DA) and norepinephrine (NE) concentrations in nucleus accumbens (NACB) and is associated with reduction in cold water restraint-induced gastric mucosal injury, inhibition of basal gastric acid output, and regional gastric mucosal blood flow. Similar effects were not observed with administration of MAO A inhibitors. These observations suggest that activation of central dopamine and norepinephrine receptors, particularly in NACB, are involved in the control of gastric mucosal function.

Increased dopamine receptor binding in duodenal mucosa of duodenal ulcer patients

High-affinity and saturable membrane-bound dopamine binding sites have been characterized in rat and human gastrointestinal tissues. Although their role in experimental ulcerogenesis has been suggested, dopamine receptor activity in peptic ulcer disease has not been investigated. Radioligand binding studies were performed with mucosal tissue homogenates obtained from the antrum and duodenum of six male healthy volunteers and six male duodenal ulcer patients. The binding assay was performed in triplicate with a crude membrane fraction using [3H]dopamine as a ligand at a final concentration of 1 nM at 22 degrees C in the dark. Nonspecific binding (which usually comprised about 30% of total binding) was determined in the presence of a 100-fold excess of unlabeled dopamine. A significant (P less than 0.05) increase of [3H]dopamine binding was found in duodenal mucosa of duodenal ulcer patients. [3H]Dopamine binding in stomach (antrum) of normal and duodenal ulcer patients did not differ significantly. These findings provide preliminary evidence for a role of dopamine receptors in duodenal ulcer and suggest that biochemical abnormalities of gut dopamine function may be operative in the pathogenesis of peptic ulcer disease.

The influence of dopamine agonists and antagonists on indomethacin lesions in stomach and small intestine in rats

Dopamine agents (saline in control groups) were coadministered with indomethacin by either single or repeated application. The ulcerogenic effect (erosions and/or ulcers) of repeated given indomethacin on gastric mucosa differed clearly from that on intestinal mucosa. The effect on intestinal mucosa was markedly greater than after a single dose. The effects of dopamine agents appeared to be more consistent. Domperidone and haloperidol, given as single or repeated doses, strongly aggravated both the gastric and intestinal lesions. Bromocriptine and amantadine had a protective effect. The adverse effects of both dopamine antagonists (increased after repeated administration) were strongly inhibited by the simultaneous administration of either bromocriptine or amantadine. The involvement of the dopamine system (central or peripheral) in the mechanisms that maintain gastric (probably related to cytoprotection also) and intestinal mucosa integrity is therefore suggested.

Effect of furazolidone on gut catecholamine in cysteamine-induced duodenal ulcer in the rat

The effect of furazolidone, a monoamine oxidase (MAO) inhibitor, on cysteamine-induced duodenal ulcer and gut catecholamines was studied in rats, since previous reports have suggested protective effects of MAO inhibitors against other forms of experimental mucosal injury. Furazolidone (100 mg kg-1, orally) pretreatment significantly reduced the frequency and severity of cysteamine-induced duodenal ulcer. By means of a spectrofluorometric technique, gastric and duodenal norepinephrine concentrations and duodenal dopamine concentrations were measured and found to be increased in animals treated with the MAO inhibitor. It is concluded that the protective effect of furazolidone against cysteamine-induced duodenal ulcer may in part be related to modulation of gut norepinephrine and dopamine concentrations.