Prevention of stress-induced gastric ulcers by dopamine agonists in the rat

Dopamine (DA) and DA agonists have been shown to exert a protective role against the formation of duodenal ulcers. The effect of stimulation of DA receptors on the development of stress-induced gastric ulcers is currently unknown. Accordingly, we evaluated the effect of several DA agonists on the development of gastric ulcers induced by 3 h of cold + restraint stress (CRS) in rats. Apomorphine, d-amphetamine, methylphenidate, and threo-dl-p-hydroxymethylphenidate (an hydroxylated analog of methylphenidate), significantly reduced both the incidence and severity of CRS-induced gastric ulcers. The gastric cytoprotection afforded by these agents was dose-related, and completely antagonized by pretreatment with the peripheally acting DA antagonist domperidone. Because domperidone blocks peripheral, but not central, DA receptors, and since the entry of threo-dl-p-hydroxymethylphenidate across the blood-brain barrier into the brain is restricted to a great extent, we conclude that stimulation of peripheral DA receptors is primarily involved in the gastric cytoprotection induced by dopamimetics.The pathogenesis of stress-induced gastric ulcers remains largely unknown, and significant efforts have been made over the last decade to functionally characterize some of the factors involved in the etiology of this disease. Considerable attention has been focused on gastric acid secretion, but its primary role in stress-induced gastric ulcer disease remains uncertain. In fact, agents which effectively inhibit or neutralize gastric acid secretion such as cimetidine or antacids do not necessarily exert protection against stress-induced gastric ulcers (1,2). Moreover, in our original studies with neurotensin, a brain and gastrointestinal peptide, we have found that central administration of this neuropeptide, which completely prevents the development of cold + restraint stress (CRS)-induced gastric ulcers, does not appreciably alter gastric acid secretion (2). These findings support the contention that gastric acid secretion may not be an important factor in the development of this type of gastric ulcer.There is, however, considerable evidence that the automatic nervous system plays an intermediary role in the development of these ulcers (3,4). In this regard, surgical or pharmacological blockade of the vagal (cholinergic) division of the autonomic nervous system prevents the appearance of stress-associated gastric ulcers (5,6). Direct stimulation of catecholamine receptors, or indirect activation via increased sympathetic outflow to the periphery (7,4,8–11) appears to produce a salutary effect of stress-induced gastric ulcers.Szabo and his associates (12, 13, 14) have extensively studied the anti ulcer effects of dopamine (DA) in duodenal ulcer formation. Whether DA also modifies the development of stress-induced gastric ulcers is currently unknown.We have therefore evaluated the effect of selected DA receptor agonists and antagonists on CRS-induced gastric ulcer formation in rats.     

Dynamics of changes in vascular endothelial growth factor (VEGF) expression and angiogenesis in stress-induced gastric ulceration in rats.

Angiogenesis and VEGF play a major role in many repair processes such as healing of gastric ulceration.The present study was undertaken to assess the dynamics of changes in VEGF expression and angiogenesis in stress-induced gastric ulcers in rats. Acute gastric ulceration was induced using a water-immersion and restraint stress method. The VEGF expression, angiogenesis, size of area and depth of ulcers in gastric specimens were evaluated. The study shows that as early as one day after the development of ulcers there is a significant increase in both the expression of the VEGF protein and the number of newly formed microvessels, while an abrupt decrease in VEGF expression, observed on the fifth day, results in a decreased intensity of angiogenesis. Moreover, it has been demonstrated that the increase in VEGF expression and angiogenesis is accompanied by a reduction in the size of area and depth of stress-induced ulcers in rats. Six days after ulcer development both VEGF expression and angiogenesis return to normal levels.     

Modifications induced through beta receptors in adrenergic nervous system and gastric ulcers (author's transl)]

The experimental relation between adrenergic nervous system and ulcus has been studied. Administration of adrenaline to rats did not induce any ulcers, or showed any noteworthy modification in the studied pH, acidity and peptic activity of gastric content parameters. The number of ulcers induced by the Shay method, acidity and peptic activity decreased after beta receptor blockage. Ko-592 did not induce any significant change on these parameters when the animals were subjected to stress conditions by restraint. Beta receptors discretely participate in ulcer pathology.     

Prolactin inhibits the development of stress-induced ulcers in the rat

Hyperprolactinaemia, as induced by pituitary homografts under the kidney capsule, was accompanied by an inhibition of development of gastric ulcers following the application of cold-plus-restraint stress in male rats. This effect was mimicked by intracisternal administration of a low dose of the hormone. Peripheral injection of the dopamine receptor antagonist, domperidone, also inhibited the development of stress-induced ulcers. However, no effect was found after peripheral injection of another dopamine receptor antagonist, haloperidol. This latter drug appeared to antagonize the cytoprotective effect of prolactin (PRL) on stress-induced ulcers. Furthermore, peripheral injection of the prostaglandin synthesis inhibitor, indomethacin, increased the incidence of gastric ulcers in hyperprolactinaemic rats subjected to cold -plus-restraint stress. These data suggest that the cytoprotective effect of PRL on development of gastric ulcers in stressed animals may involve both central (i.e. dopamine transmission) and peripheral (i.e. prostaglandin synthesis) mechanisms.     

Immunocytochemically detectable metallothionein in granulation tissue surrounding mucosal ulceration

Summary Metallothioneins (MTs) are low-molecular-weight heavy metal binding proteins which are effective free oxygen radical scavengersin vitro. Free oxygen radicals have been implicated in the pathogenesis of stress-induced acute gastric mucosal ulceration and ischaemic injury in rat and man. Experimentally, MTs can have a protective role in stress-induced ulceration in rats. The possible cytoprotective role of MTs in chronic mucosal ulceration in man has not been previously studied. Evidence for locally produced MTs in human chronic gastric and small bowel ulcers has been sought by immunocytochemical staining using a monoclonal antibody (E9) to MT. At the base of ulcers MT has been localized to spindle cells (fibroblasts) in granulation tissue. Labelling of macrophages with a pan-macrophage marker KP1, and double labelling with KP1 and E9 showed two distinct populations, and MT appeared to be localized primarily in fibroblast-like cells.     

Brain corticotropin-releasing factor acts as inhibitor of stress-induced gastric erosion in rats

Gastric lesions are known to be caused by stress. Corticotropin-releasing factor (CRF) is a key peptide initiating various stress response. This study was designed to investigate how brain CRF is involved in the occurrence of stress-induced gastric erosion in rats. Intracerebroventricular (icv) administration of CRF suppressed the occurrence of gastric erosion induced by water-immersion restraint stress, and its suppressive effect was blocked by coadministration of a CRF receptor antagonist in rats. The peripheral administration of CRF had no influence on the occurrence of erosion. The icv administration of a CRF receptor antagonist or anti-rat CRF gamma-globulin increased gastric erosion induced by the stress. Ganglionic blockade with chlorisondamine, muscarinic blockade with atropine, or bilateral adrenalectomy by itself significantly inhibited the occurrence of stress-induced gastric erosion, and no additional effect of CRF on these treatments-induced inhibition of erosion was found. These results, therefore, suggest that the occurrence of stress-induced gastric erosion is mediated by the autonomic nervous system- and adrenal-dependent pathway, and that brain CRF reduces the occurrence of stress-induced gastric lesions by acting on its specific receptor within the central nervous system, probably through the autonomic nervous system- and adrenal-dependent mechanism.     

Prostaglandins VIII: A proposed role for PGE2 in the genesis of stress-induced gastric ulcers

A protective effect on stress-induced gastric ulcers has been d monstrated for PGE₂ and PGF_2α in rats. Pretreatment with indomethacin 5 mg/kg/per os increases the severity of gastric lesions, but this effect is completely antagonized by PGE₂ administration.     

Potent CNS action of calcitonin to inhibit cysteamine-induced duodenal ulcers in rat

Intracisternal injection of calcitonin (0.01-5 micrograms) dose dependently prevented the development of duodenal ulcers induced by cysteamine in female rats. By contrast, intravenous infusion of the peptide at a dose 50 times higher than an effective intracisternal dose, had no effect. Intracisternal injection of calcitonin increased by three fold the generation of 6-keto-PGF1 alpha, the stable hydrolysis product of PGI2, in the duodenal mucosa. These studies demonstrated that calcitonin acts within the brain to potently suppress duodenal ulcers induced by cysteamine. The mechanisms of the antiulcer effect may involve changes in prostaglandin generation along with alterations of gastrointestinal secretion and motility associated the central injection of calcitonin. Growing evidence suggests that salmon calcitonin may act as a neuromodulator or neurotransmitter in the central nervous system. Specific binding sites have been demonstrated for calcitonin in the hypothalamus, brain stem and dorsal horn of the spinal cord using homogenate and membrane preparations or in vitro autoradiography methods. The peptide injected into the cerebrospinal fluid (CSF) produces a wide spectrum of biological effects including analgesia, hyperthermia, changes in pituitary hormone release, decrease in food and water intake, locomotor activity, and blood pressure. Numerous studies also demonstrated that calcitonin acts within the brain to markedly influence gastrointestinal secretory and motor function in rats and dogs and gastric ulceration in rats. In particular, intracisternal injection of salmon calcitonin was found very potent to selectively inhibit gastric ulcers elicited by stress, aspirin and central thyrotropin-releasing factor but not by necrotizing agents. In the present study, we further investigated the antiulcer effect of salmon calcitonin using the well established cysteamine experimental model to induce duodenal ulcers in rats. Part of this work has been reported in abstract form.     

Characterization of "unhealed gastric ulcers" produced with chronic exposure of acetic acid ulcers to indomethacin in rats.

We previously discovered that a 4-wk course of indomethacin delivered to rats with acetic acid ulcers resulted in production of "unhealed gastric ulcers" that persisted for up to 12 wks after treatment cessation. The present study examined the mechanism underlying such "unhealed gastric ulcers" with biochemical and histological procedures. "Unhealed gastric ulcers" were induced with a 4-wk indomethacin treatment (1 mg/kg, twice daily) in rats with acetic acid ulcers. Two and 4 wks after treatment cessation, ulcer size was significantly larger in rats receiving indomethacin compared with control animals. Ulcerated tissue prostaglandin E2 levels were significantly lower during indomethacin treatment, but the levels tended to increase after treatment cessation compared with levels measure in the group receiving vehicle. Myeloperoxidase activity levels were significantly higher during indomethacin treatment; such levels persisted after treatment cessation. Histologically, greater degrees of fibrosis and neutrophil accumulation, as well as a lesser degree of angiogenesis were observed in the "unhealed gastric ulcers" compared to ulcers that healed in a normal fashion. It was concluded that severe fibrosis, persistent neutrophil infiltration, and poor angiogenesis in the ulcer base might represent factors involved in the mechanism underlying production of "unhealed gastric ulcers".     

Central basic fibroblast growth factor inhibits gastric ulcer formation in rats

We have recently reported that basic fibroblast growth factor (bFGF) acts in the brain to inhibit the secretion of gastric acid and pepsin, two major aggressive factors in the pathogenesis of gastric ulcer formation. In the present study, we determined whether or not bFGF has an anti-ulcer action via the central nervous system, using male Wistar rats. The intracisternal injection of bFGF dose-dependently (0.1-1.0 microgram(s)/rat) inhibited the severity of gastric ulcers induced by water-immersion restraint stress or central thyrotropin-releasing hormone. The same doses of peripherally injected bFGF failed to protect the gastric mucosa from these ulcerogenic procedures. These results suggest for the first time that bFGF has a mucosal protective effect through a mechanism involving the central nervous system. It is speculated that this anti-ulcer action of bFGF is, at least in part, dependent upon its gastric antisecretory effect.     

Role of dopamine receptors in the mechanism of formation of stress-induced stomach lesions

Experiments on rats with the use of different exposures to stress (generalized electrization and "social stress") have demonstrated that stimulation of dopamine receptors localized in the central nervous system is one of the reasons for stress-induced gastric lesions, particularly for massive hemorrhages. Stimulation of peripheral dopamine receptors seems to have a gastroprotective action. As judged from the intensity of the effects of the dopamine agonists, apomorphine and L-DOPA, on stress-induced lesions of the gastric mucosa, stimulation of D2- rather than of D1-dopamine receptors is of greater importance in stress.     

Interleukin-1 inhibits stress-induced gastric erosion in rats

The effect of interleukin (IL)-1 on the occurrence of stress-induced gastric erosions was examined in rats. The intracerebroventricular (icv) administration of IL-1 beta significantly inhibited the occurrence of water-immersion restraint stress-induced gastric erosion at doses of 200 ng, 500 ng and 1 microgram, whereas the intravenous (iv) administration of IL-1 beta altered the occurrence of gastric erosion only at a dose of 1 microgram. The inhibitory effect of IL-1 alpha icv administered on the occurrence of gastric erosion was found only at a dose of 1 microgram. The inhibitory effect of IL-1 beta icv administered on the occurrence of stress-induced gastric erosion was not influenced by icv administration of alpha-helical CRF(9-41), a corticotropin-releasing factor (CRF) receptor antagonist. Indomethacin completely blocked the inhibitory action of IL-1 beta icv administered on stress-induced gastric erosion. It is concluded from these results that IL-1 acts mainly in the central nervous system to inhibit the occurrence of stress-induced gastric erosion and that the IL-1 beta-induced inhibition of gastric erosion is mediated by prostaglandin in a manner that is independent of brain CRF.     

Adrenergic and cholinergic innervation of the prostate in laboratory animals

The prostate innervation has been studied in 50 white rats, 12 rabbits, 12 guinea pigs, 6 cats and 6 dogs. Together with the impregnation techniques, Karnovsky-Roots method has been applied, for revealing cholinergic components, and the incubation method in 2% solution of glyoxylic acid, for revealing adrenergic nervous structures. Density of adrenergic and cholinergic nervous plexuses has been estimated by means of the planimetric point method. The prostate of the laboratory animals possesses well manifested adrenergic and cholinergic nervous plexuses. The organ's alveolus and ducts are covered with adrenergic and cholinergic fibers, however, the relative density of the cholinergic plexuses is less than that of the adrenergic ones. The guinea pig prostate is the most richly supplied with the adrenergic nervous plexuses, and the rabbit prostate--with the cholinergic nervous plexuses.     

Effect of indomethacin on opioid-induced gastric protection in cold-restrained stress

Morphine and the synthetic opioid met-enkephalin analog [D-Ala2, MePhe4, Met(0)5ol] enkephalin (FK 33-824) injected intraperitoneally to rats at doses of 5-20 and 0.5-2 mg/kg respectively showed a protective effect on gastric lesion induced by cold-restraint stress. This protective effect was abolished by pretreatment with indomethacin. This suggests a role for prostaglandins in the protection, induced by opioids of the gastric mucosa against the development of stress-induced ulcers.     

Gastro-protective and Anti-stress Efficacies of Monomethyl Fumarate and a <Emphasis Type="Italic">Fumaria indica</Emphasis> Extract in Chronically Stressed Rats

Results of the very first experiments conducted to evaluate therapeutic potentials of a fumarate containing Fumaria indica extract and of fairly low daily oral doses of monomethyl fumarate for prevention of chronic unavoidable foot-shock stress-induced gastric ulcers, and possible involvement of diverse neuro-hormonal and oxidative process in their stress response desensitizing effects are reported and discussed in this article. Preventive effects of 21 daily oral 60, 120, and 240 mg/kg doses of a standardized 50 % methanolic F. indica extract (MFI) and 1.25, 2.50, and 5.00 mg/kg/day of pure monomethyl fumarate (MMF) were compared in rats subjected to one hour daily unavoidable foot-shocks. A pharmaceutically well-standardized Withania somnifera (WS) root extract was used as a reference herbal anti-stress agent in all experiments. Effects of the treatments on stress-induced alterations in body weight, adrenal and spleen weights, gastric ulcer and ulcer index, weight of glandular stomach, protective mucosal glycoprotein content, cellular proliferation, oxidative stress on stomach fundus, and brain tissues of male rats were quantified. Other parameters quantified were plasma corticosterone levels, brain monoamine levels, and expressions of the cytokines TNF-α, IL-10, and IL-1β in blood and brain of stressed and treated rats. Most but not every observed stress-induced anomalies were suppressed or completely prevented by both MFI and pure MMF treatments in dose-dependent manner. Qualitatively, the observed activity profiles of both of them were similar to those of WS dose tested. These results reveal that both MFI and MMF are potent gastro-protective agents against chronic unavoidable stress-induced ulcers and strongly suggest that they act as regulators or modulators of monoamine, corticosterone, and cytokine homeostasis.     

Antiulcerogenic activity of Satavari mandur--an Ayurvedic herbo-mineral preparation

Satavari mandur (SM) is a herbo-mineral preparation containing Asparagus racemosus, which finds mention in ancient Indian texts for treatment of gastric ulcers. The ulcer protective effect of SM, 125-500 mg/kg given orally, twice daily for three, five and seven days, was studied on cold restraint stress-induced gastric ulcer in rats. The effective regimen was found to be 250 mg/kg given for five days and hence was used for further experiments. SM showed significant protection against acute gastric ulcers induced by pyloric ligation but was ineffective against aspirin- and ethanol-induced ulcers. Further, gastric juice studies showed that, SM significantly increased the mucosal defensive factors like mucus secretion, but had little or no effect on offensive factors like acid and pepsin secretion.     

Gastroprotective and Anti-oxidative Properties of Ascorbic Acid on Indomethacin-induced Gastric Injuries in Rats

Reactive oxygen species (ROS) have been implicated in the etiology of indomethacin-induced gastric mucosal damage. This study investigated ascorbic acid (vitamin C)'s protective effects against oxidative gastric mucosal damage induced by indomethacin. Ascorbic acid is a powerful antioxidant because it can donate a hydrogen atom and form a relatively stable ascorbyl free radical. We have investigated alterations in the levels of myeloperoxidase, antioxidant system enzymes (glutathione S-transferase, superoxide dismutase, glutathione reductase, catalase, glutathione peroxidase), lipid peroxidation and glutathione, as markers for ulceration process following oral administration of ascorbic acid, famotidine, lansoprazole, and ranitidine in rats with indomethacin-induced ulcers. In the present study, we found that (1) ascorbic acid, famotidine, lansoprazole and ranitidine reduced the development of indomethacin-induced gastric damages; (2) the administration of indomethacin caused a significant decrease in the levels of superoxide dismutase, glutathione peroxidase, glutathione S-transferase and glutathione, and an increase in the lipid peroxidation level; (3) the administration of ascorbic acid reversed the trend, inducing a significant increase of these enzymes' levels and a reduction in lipid peroxidation level in tissues; and (4) catalase, glutathione reductase and myeloperoxidase activities, increased by indomethacin, were found to be lower in the ascorbic acid, famotidine, lansoprazole and ranitidine-treated groups. The results indicate that the gastroprotective properties of ascorbic acid could be related to its positive effects on the antioxidant system and myeloperoxidase activity in indomethacin-induced gastric ulcers in rats.     

Corticotropin-releasing factor antagonist blocks stress-induced fighting in rats

Corticotropin-releasing factor (CRF) has been shown to have potent central nervous system-activating effects when administered intracerebroventricularly (i.c.v.). In the present experiment, this activating effect was exaggerated by use of a stress-motivated behavioral paradigm. Low doses of CRF (0.01 and 0.1 micrograms/rat) administered i.c.v. facilitated stress-induced fighting. More importantly, alpha-helical CRF-(9-41), a CRF antagonist, blocked stress-induced fighting produced by higher levels of stress. These results suggest that CRF in the central nervous system may have a role in mediating behavioral responses to stress.     

Antiulcer activity of Salvadora persica L.: structural modifications.

In previous work we observed that the decoction of Salvadora persica L. possessed significant protective action against ethanol and stress-induced ulcers. This study was designed to confirm the antiulcer activity of Salvadora persica decoction using optical microscopy. The elements of gastric mucosa tended to be reestablished normally in treated rats.