Gastric ulcers induced by acid accumulation and by stress in pylorus-occluded rats

Circadian reactivity rhythm of rat gastric mucosa to restraint-cold stress and indomethacin: temporal variation in the protective effect of iloprost

In this study, the time-dependent ulcerogenic effects of restraint-cold stress and indomethacin on the gastric mucosa and the temporal variation in the protective effect of iloprost, a synthetic stable analog of prostacyclin, were investigated in rats synchronized to 12h light and 12h darkness, lights on at 08:00. The severity of gastric ulceration produced by either stress or indomethacin showed marked circadian variation; it was greatest at 11 HALO (hours after lights on) for restraint-cold stress and at 23 HALO for indomethacin. The severity of the induced ulcerogenesis was least at 7 HALO for both stimuli. The protective effect of iloprost against restraint-cold stress was most prominent at 15 HALO and 19 HALO with an approximately 80% protection score. On the other hand, pretreatment with iloprost reduced the indomethacin-induced mucosal injury only at 23 HALO. The circadian variation in the effect of iloprost and in the rhythmic modalities of these two experimental ulcer models are indicative of differences in their underlying mechanisms. In experimental models of ulceration, the circadian time of application of the ulcerogenic stimulus must be considered as an important experimental factor. Moreover, the protective effectiveness of antiulcer drugs can express time-dependent differences and must also be taken into account in investigative research.

Effect of evening primrose oil on gastric ulceration and secretion induced by various ulcerogenic and necrotizing agents in rats

The evening primrose oil (EPO) commercially known as Callanish evening primrose oil (omega-6 polyunsaturated fatty acid) is linoleic acid (LA) and gamma-linolenic acid (GLA)-enriched oil obtained from the seeds of Oenothera biennis L. (Fam. Onagraceae). EPO was investigated for its ability to protect the gastric mucosa against injuries caused by pylorus ligation, non-steroidal anti-inflammatory drugs (NSAIDs; aspirin, indomethacin and phenylbutazone), hypothermic restraint stress and necrotizing agents [0.6 M HCl, 0.2 M NaOH, 25% NaCl or 80% (v/v) aqueous ethanol]. It was administered by gastric intubation at doses of 5 and 10 ml/kg body weight to rats fed standard chow diet. An additional group of animals was given the same amount of corn oil in each experimental model studied. The results showed that EPO at the doses of 5 and 10 ml/kg body weight provided significant protection in various experimental models used. It produced a significant inhibition of gastric mucosal damage induced by pylorus ligation, NSAIDs, or hypothermic restraint ulcers. EPO also had a marked cytoprotective effective effect against all necrotizing agents used in this study. The results suggest that EPO rich in LA and GLA possesses both antisecretory and anti-ulcerogenic effects.

The role of the neurotransmitters acetylcholine and noradrenaline in the pathogenesis of stress ulcers

1. Adrenergic and cholinergic mechanisms seem to be involved in the pathogenesis of stress ulcers. 2. In this study, gastric ulcers were induced in rats by immobilization and cold. Prior intraperitoneal administration of both anticholinergic (atropine) as well as alpha-blocking medication (phenoxybenzamine) produced a very significant decrease in stress ulcers. 3. Additionally, using the technique of continuous intravenous perfusion in rats, acetylcholine was shown to have a gastric ulcerogenic effect, in contrast to noradrenaline. 4. It is concluded that acetylcholine is the peripheral mediator in stress ulcers, while noradrenaline intervenes at the encephalic level in stress ulcer pathogenesis.

Nifedipine versus cimetidine in prevention of stress-induced gastric ulcers in rats

The effects of nifedipine and cimetidine on cold/restraint stress-induced gastric ulcers and glandular wall mast cell count were studied in rats. Two hours of restraint at 4 degrees C resulted in 90% ulceration rate in the glandular stomach with a decrease in glandular wall mast cell count in the mucosa, submucosa and muscle layer. Nifedipine in three doses (1, 5 and 10 mg/kg) administered i.p. 30 min before stress significantly and dose dependently prevented gastric ulceration and mast cell degranulation. Cimetidine, in doses of 50, 100 and 150 mg/kg, again administered 30 min before stress prevented only gastric ulceration dose dependently without a significant change in mast cell count. The results indicate that both nifedipine and cimetidine are equally effective to reduce gastric mucosal ulceration in response to stress. However, the unique effect of nifedipine to inhibit mast cell degranulation which was now clearly demonstrated may favour the potential value of this drug in the management of peptic ulcer disease in humans.

Neurogenic stress ulceration caused by laparotomy under anesthesia plus restraint. The device of a new rat model

We report herein, a new method devised of producing neurogenic stress ulceration in rats. An experimental subarachnoid hemorrhage (SAH) was produced in rats by injecting 0.2 ml of arterial blood from other rats into the cisterna magna. Three days later, the rats were laparotomized for 1 hour under ether anesthesia, followed by restraint for 3 hours in wakefulness. The SAH rats were found to develop stress ulcers (UL-I) in the glandular stomach, which were significantly (p less than 0.001) more marked than those in non-SAH rats. Measurements were performed on gastric acid secretion, an important aggressive factor. It was found that the SAH rats undergoing the laparotomy-restraint stress showed a more marked increase in gastric acid secretion and a more marked reduction in MBF, than the non-SAH rats. The effects of bilateral vagotomy, upper abdominal sympathectomy and bilateral adrenalectomy were examined, and it was revealed that the SAH rats were under the condition of hyperreactivity both in the sympathetic and parasympathetic systems and, on this basis, the laparotomy-restraint stress caused the stress gastric ulceration. In this rat model, the laparotomy stress was applied under anesthesia and any exposure to low temperatures which may have interfered with blood circulation was avoided.

Antiulcer activity of the calcium antagonist propyl-methylenedioxyindene. IV. Effects on gastric lesions in rats induced by cold-restraint stress and thyrotropin-releasing hormone

Propyl-methylenedioxyindene (pr-MDI; 30 mg/kg, i.p.), an intracellular calcium antagonist, significantly reduced the number and size of erosions per stomach induced by cold-restraint stress by 69% and 86%, respectively. Our previous findings indicate that the antiulcer activity of pr-MDI is highly correlated with its inhibitory effect on gastric motor activity. Since central TRH is suggested as the brain mediator responsible for cold-restraint stress gastric ulcers in rats, the inhibitory action of pr-MDI was evaluated in the TRH-induced gastric lesion model. Pr-MDI (30 mg/kg) did not reduce the gastric erosions induced by intracisternal administration of 100ng RX77368, a stable thyrotropin-releasing hormone (TRH) analogue, even though it abolished the RX77368-induced stimulation of gastric emptying, gastric acidity, and acid output. Since pr-MDI (30 mg/kg, i.p.) significantly inhibited the stimulation of gastric motility by both cold-restraint stress and TRH, but only cold-restraint stress-induced gastric erosions were effectively reduced by the drug, the present findings suggest a possible dissociation between the ulcerogenic mechanisms of cold-restraint stress and intracisternal administration of TRH.

Acute gastritis occurring within 24 hours of severe head injury

The purpose of this study was to evaluate the early appearance and incidence of stress gastritis following severe head injury. We performed upper esophagogastroduodenoscopy in 44 patients within 24 hours of a head injury. All patients were comatose and required ventilatory support. Forty of the patients (91%) had gastritis at esophagogastroduodenoscopy. The lesions were distributed in the fundus and corpus of the stomach (77% of the patients), in the esophagus (30% of the patients), in the antrum (25% of the patients), and in the duodenum (7% of the patients). The grade of gastritis at esophagogastroduodenoscopy did not correlate with the severity of the head injury, the type of head injury sustained, the timing of esophagogastroduodenoscopy after head injury, or the presence of shock on admission. However, patients with grade III gastritis had a greater injury Severity Score than patients with grade 0 gastritis (normal mucosa). Gastroduodenal mucosal damage is common after severe head injury and occurs soon after the event.

Cimetidine and ranitidine protect against cold restraint-induced ulceration in rat by suppressing gastric acid secretion

The effect of the H2-receptor antagonists cimetidine and ranitidine on pentagastrin-stimulated gastric acid secretion in anesthetized rats, and gastric mucosal lesion formation and gastric motility in unanesthetized cold-restrained rats was studied. Both cimetidine and ranitidine suppressed pentagastrin-stimulated gastric secretion in a dose-dependent fashion. Cold restraint-induced lesion formation was not prevented with doses of both agents that inhibited acid secretion by 75%. Doses which suppressed pentagastrin-stimulated acid secretion more than 90% significantly prevented the development of gastric mucosal lesions produced by cold restraint. Doses of both H2 blockers which demonstrated significant suppression of lesion formation had no effect on cold restraint-stimulated gastric contractility. We conclude that cimetidine and ranitidine suppress cold restraint-induced lesion formation by suppressing acid secretion and not by suppressing gastric contractility.

Inhibition of gastric secretion and stress-induced ulcers by intravenous Asu(1,7)eel-calcitonin independent of vasopressin

The effects of different doses of Asu(1,7) eel-calcitonin, peripherally injected, on gastric secretion were studied in conscious Brattleboro rats, which are genetically deficient in vasopressin. Moreover, we evaluated the activity of this analogue on gastric ulcer formation by restraint stress. We found that 5 IU/kg Asu(1,7) eel-calcitonin decreased gastric secretion and inhibited the development of stress-induced ulcers in Brattleboro rats. These data suggest that vasopressin does not play a role in the gastrointestinal activity of Asu(1,7) eel-calcitonin.

Luminal acid in stress ulceration and the antiulcer action of verapamil in rat stomachs

The role of luminal acid and the influence of the antisecretory action of verapamil in stress ulcer prevention in rat stomachs have been studied. Intraperitoneally injected verapamil, 4 mg kg-1, inhibited gastric acid secretion and ulcer formation, however, a 2 mg kg-1 dose, which did not significantly influence acid output, also had an antiulcer effect. Intraperitoneal injection of bethanechol, 1.2 or 3.6 mg kg-1, increased gastric acid output, but did not influence stress-induced ulcer formation. Oral administration of HCl, 25 or 50 mu equiv, aggravated stress ulceration in a dose-dependent manner; this lesion-worsening effect was prevented by pretreatment with verapamil or bethanechol. The gastric luminal acid content in 2 h pylorus-ligated rats was similar in the groups given either bethanechol or HCl. These findings indicate that the antisecretory action of verapamil may not account for its antiulcer effect. It is suggested that endogenous and exogenous luminal acid may have different influences on stress ulcer formation.

Effects of morphine, hypoxaemia and hypercapnia on the rat stomach

The effects of morphine, hypoxaemia or hypercapnia on gastric acid secretion, gastric mucus synthesis and the gastric mucosa were studied in conscious rats with pyloric occlusion. Hypoxaemia and hypercapnia were induced by morphine 32 mg/kg given i.p., or each condition was produced separately by adjusting the composition of respired air in the chamber where the animals were kept during the experimental period. Hypoxia significantly enhanced gastric mucus synthesis whereas hypercapnia significantly reduced gastric acid secretion. These effects were significantly alleviated by atropine pretreatment. Morphine-treated rats exhibited decreased gastric acid secretion, increased gastric mucus synthesis and a higher mean ulcer index but only the reduced gastric acid output was significantly prevented by atropine. It is suggested that the effect of morphine on gastric acid secretion may result from its respiratory depressant action and consequent acute stress production. However, the mechanisms by which morphine can increase mucus synthesis and produce ulceration remain obscure.

Prostaglandin requirements are greater for protection in cold restraint-induced than alcohol-induced gastric mucosal injury

Exogenous prostaglandins inhibit visible gastric mucosal lesions produced by both absolute ethanol and cold restraint in the rat. Pretreatment with "mild irritants" significantly reduces the magnitude of ethanol-induced lesions presumably by stimulating endogenous prostanoid production. The effect of mild irritant pretreatment on cold restraint-induced lesion formation has not been previously reported. This study was designed to compare the protective effect of pretreatment with two "mild irritants," 4% NaCl and 0.35 M HCl, and the synthetic prostanoid, 16,16 dimethyl PGE2(16,16-dm PGE2), on lesions produced by cold restraint or absolute ethanol. Pretreatment with both mild irritants produced complete visible protection against ethanol-induced injury but had variable effects against cold restraint-induced injury. Whereas 5 micrograms/kg 16,16-dmPGE2 provided complete visible protection against ethanol-induced injury, 20 micrograms/kg 16,16-dmPGE2 was required for complete visible protection against cold restraint-induced injury. We conclude that prostaglandin requirements for protection against cold restraint injury are greater than for protection against ethanol-induced gastric mucosal injury.

Gastric acid secretion and lesion formation in rats under water-immersion stress

In attempts to investigate the roles of acid in the pathogenesis of stress-induced gastric lesions, gastric acid secretion was studied in pylorus-ligated and lumen-perfused rats under restraint alone (R) or restraint with additional water immersion (WI). Gastric mucosal blood flow (GMBF) was measured with the aminopyrine clearance method in acute fistula rats. Acid secretion in pylorus-ligated rats significantly decreased under R or WI of either 3.5 or 7 hr stress. In the lumen-perfused or acute-fistula rats, exposure of rats to stress for 7 hr produced a similar decrease; however, in the WI group, there was a significant increase of acid secretion for 3-4 hr during stress, but not exceeding the prestress level. Only in the WI group did GMBF exhibit similar increases to those of acid secretory activity, and these increases were significantly inhibited by intraperitoneal administration of atropine (1 mg/kg) or cimetidine (60 mg/kg). Gastric lesions developed in both groups at 3.5 hr and became extensively severe at 7 hr only in the WI group. Cimetidine failed to influence the formation of lesions at 3.5 hr but significantly inhibited the later outgrowth of lesions at 7 hr, while atropine or pylorus ligation all but completely prevented lesions induced by either 3.5- or 7-hr WI stress. These results indicate that exposure of rats to stress (R or WI) generally decreased acid secretory activity, but there was a rise in acid secretion toward normal levels during WI stress, which may play an important role in the aggravating process of stress-induced gastric lesions.

Mechanisms of acute gastric mucosal lesion accompanying obstructive jaundice--role of bile acids in plasma

The mechanism of acute gastric mucosal lesion (AGML) accompanying obstructive jaundice was studied in male Wistar rats, with special reference to the effect of bile acids in plasma on mucosubstances in the gastric mucosa. Following ligation of the common bile duct, total plasma level of bile acids increased 24 folds over the control level, and gastric mucosal mucus contents, measured biochemically or histochemically, significantly decreased. Effect of increased bile acids in the blood stream on the gastric mucosa was estimated by continuous intravenous administration of sodium taurocholate. After 24 hours infusion, both gastric acid output and gastric mucus contents significantly decreased. Further imposition of restraint and water immersion stress produced AGML significantly earlier than in control rats with continuous intravenous infusion of 0.9% NaCl. These data suggest that the increased plasma level of bile acids play an important role on the reduction of the gastric-mucosal defense mechanism in obstructive jaundice directly through their toxic effects, and that this easily results in the formation of AGML under additional stresses.

Inhibition of restraint stress by systemic (Asu1,7) eel-calcitonin

The effects of different doses of (Asu1,7) eel-calcitonin, iv injected, on gastric secretion were studied in conscious rats with pyloric occlusion. Moreover, we evaluated the activity of this analogue on gastric ulcer formation by restraint stress. It was found that 2.5 or 5 Ul/kg (Asu1,7) eel-calcitonin decreased gastric acid secretion and inhibited the development of stress-induced ulcers in rats. In the isolated rat stomach the peptide at the concentrations of 1 nM to 1 microM did not modify acetylcholine, histamine or 5-hydroxytriptamine-induced contractions. These results suggest that this peripheral activity of (Asu1,7) eel-calcitonin does not involve a direct interference with cholinergic, histaminergic or serotonergic pathways at gastric level.

Sulphasalazine and experimental stress ulcers

The effects of sulphasalazine on gastric ulceration induced by restraint at 4 degrees C (stress) for 2 h were studied in rats. Doses of 63 or 125 mg/kg s.c., which had no effect on stomach wall prostaglandin E2 (PGE2) levels, prevented stress ulceration but not the lesions produced by indomethacin. Stress significantly increased gastric glandular mucosal PGE2 levels. Indomethacin pretreatment (20 mg/kg, p.o.) markedly reduced PGE2 levels in the same region of the stomachs, and worsened stress-induced lesion formation. Pretreatment with sulphasalazine of animals given indomethacin and then subjected to stress did not appear to affect the indomethacin component of indomethacin-stress ulceration. Oral administration of PGE2 200 micrograms/kg significantly elevated gastric PGE2 levels, but had no effect on stress ulceration. It appears that neither the antiulcer activity of sulphasalazine nor stress-induced ulceration is associated with gastric tissue PGE2 increase or decrease, respectively. The protective mechanism may result from the ability of sulphasalazine to inhibit lipoxygenase activity.

Protective effect of GABA and sodium valproate on stress-induced gastric lesions in guinea-pigs

gamma-Aminobutyric acid (GABA) and sodium valproate (VPA) inhibit the formation of stress-induced gastric ulcers in guinea-pigs. The present study was conducted to evaluate the effect of these drugs on the development of cold- and restraint-induced gastric ulcers in guinea-pigs. In control saline-pretreated animals, a 3 h exposure to cold and restriction resulted in the production of gastric ulcers in 9 out of 10 animals. GABA (200 mg kg-1 oral, i.p.) completely prevented the development of gastric ulcers. VPA (100 and 200 mg kg-1 i.p.) exerted no significant effects on the development of gastric ulcers. GABA (100 mg kg-1 oral and i.p.) and VPA (oral) also exhibited partially protective activity. It is suggested that GABA may participate in a physiological modulation of the gastric mucosal barrier, by increasing its resistance to stress-induced lesions.

Intracerebroventricular injection of a TRH analogue, gamma-butyrolactone-gamma-carbonyl-L-histidyl-prolinamide, induces gastric lesions and gastric acid stimulation in rats

The effects of TRH and its biologically stable analogue, gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide (DN-1417), on gastric mucosa and acid secretion were examined in rats. Intracerebroventricular (ICV) injection of DN-1417 (0.1-10 micrograms) caused a dose-dependent gastric lesion in the corpus and antrum 6 h after administration. The gastric lesions produced by 1 microgram of DN-1417 were more severe than those produced by ICV TRH (10 micrograms), intravenous DN-1417 (200 micrograms) and stress. Although the lesion-generating effect of TRH (10 micrograms) tended to be reduced 6 h after the injection, that of DN-1417 (1 microgram) was sustained during 6 h. Atropine (0.1 and 1 mg/kg s.c.) inhibited DN-1417-induced gastric lesions in a dose-related manner while sulpiride (10 and 30 mg/kg s.c.), haloperidol (1 mg/kg i.p.), phentolamine (1 and 5 mg/kg s.c.) and yohimbine (5 mg/kg s.c.) did not prevent the lesions. ICV DN-1417 also stimulated basal gastric acid secretion and the effect was stronger and longer-lasting than that of TRH. Atropine (0.1 mg/kg s.c.) stopped DN-1417-stimulated gastric acid secretion. In conclusion, the possibility that TRH may be involved in the CNS modulation of gastric mucosal integrity deserves further attention. The enhanced potency of action of DN-1417 over TRH could make ICV injection of this peptide a useful tool for inducing centrally-mediated gastric lesions in rats.

The influence of verapamil on the gastric effects of stress in rats

The influence of verapamil on stress- or bethanechol-induced gastric effects was investigated in rats. Intraperitoneally injected verapamil (1, 2 or 4 mg/kg), given 30 min beforehand, dose-dependently prevented gastric glandular ulceration, mast cell degranulation and the increased stomach wall contractions evoked by restraint at 4 degrees C for 1 h. Gastric acid secretion, as well as ulceration in both the forestomach and glandular segment, produced by subcutaneously-injected bethanechol (3.2 mg/kg) were also inhibited. It is concluded that decreased amine release from the mast cells, stomach wall relaxation and reduced gastric acid were responsible for the ulcer-antagonising effects of the calcium-entry blocker. The possible antiulcer actions of verapamil are discussed in the light of present knowledge regarding calcium involvement in the various mechanisms thought to contribute to the pathophysiology of stress ulceration in rat stomachs.

The aetiology of gastric ulceration induced by electrical vagal stimulation in rats

Histamine and serotonin levels in gastric secretion and the effects of pharmacological antagonists were studied in rats in which stomach ulceration was induced by electrical vagal stimulation. Electrical vagal stimulation (2 and 5 V) produced a graded increase in haemorrhagic glandular mucosal ulcers. NaHCO3 perfusion completely neutralised the increased acid output but failed to prevent ulceration. Atropine inhibited gastric mast cell degranulation as well as histamine and serotonin release. Diphenhydramine, atropine and sub-diaphragmatic vagotomy antagonised the increase in intragastric pressure. Diphenhydramine, cimetidine, atropine or vagotomy but not methysergide reduced ulcer severity. It is concluded that gastric acid and serotonin do not play an important role in glandular ulceration induced by electrical vagal stimulation. The lesions probably result from increased intragastric pressure and release of gastric histamine which stimulates H1 and H2 receptors in the stomach. The similarities between the aetiologies of glandular ulcers due to electrical vagal stimulation and to stress are also discussed.

The gastric antisecretory activity of 3-methoxy-5,7,3'4'-tetrahydroxyflavan (ME)--a specific histidine decarboxylase inhibitor in rats

3-Methoxy-5,7,3'4'-tetrahydroxyflavan (ME), a specific histidine decarboxylase inhibitor, has been shown to significantly reduce the gastric acid secretion and gastric tissue histamine levels in 6 h pylorus ligated rats. It has been found to be as effective as cimetidine in reducing the gastric acid secretion. However, cimetidine does not affect the gastric tissues histamine levels in the normal or pylorus ligated rats. These observations clearly establish that the two drugs reduce the gastric acid secretion by different mechanisms and suggest that their combination may show a potentiated gastric anti-ulcer activity.

Decreased acid secretion and gastric lesion production by morphine in rats

The effects of graded doses of morphine on gastric secretion were studied in conscious rats with pyloric occlusion. It was found that, at doses which significantly prolonged the reaction time in the tail-immersion test, morphine significantly decreased both the volume and total acid output of gastric secretion. It was also observed that morphine produced gastric mucosal lesions in a dose-dependent manner. Pretreatment with naloxone 4 mg/kg significantly alleviated the gastric effects of morphine 32 mg/kg. It is suggested that the depressant effects of morphine on gastric secretion and the ulcerogenicity of the narcotic result from its stimulant activity on opiate receptors.

Effects of catecholamine agonist and antagonist drugs on acute stomach ulceration induced by medial hypothalamic lesions in rats

In order to investigate the involvement of catecholamines (CAs) in acute stomach ulceration induced by hypothalamic lesions, rats were given bilateral electrolytic anodal lesions in the medial hypothalamus followed by a single subcutaneous injection of CA agonist or antagonist drugs. As in previous studies, lesioned rats that received no post operative drug treatment showed extensive gastric damage when examined 24 hr after the brain lesion. Chlorpromazine, amphetamine, desipramine and isoproterenol caused significant reductions in the extent (total length) and/or number of erosions induced by the brain lesion. Haloperidol and propranolol did not seem to affect ulcer formation. Clozapine increased the number but not the total length of ulcers. Phentolamine, alone or in combination with propranolol, significantly increased both the number and total length of lesion-induced ulcers. Similarities between these results and those reported for most of these drugs in the context of ulcers induced by various experimental stress procedures suggest a degree of commonality between acute stress ulcers and ulcers induced by hypothalamic lesions. The overall pattern of results obtained is also consistent with evidence indicating a protective role for catecholamines in acute ulcer formation.

Different mode of action of cimetidine and prostaglandin on the rat gastric mucosa under stress loading by restrain and water-immersion

Gastric mucosal blood flow and oxygen tension in the corporal mucosa gradually declined after water immersion in the control animals. Neither cimetidine nor prostaglandin E2 had any influence on the decrease of the corporal mucosal blood flow or mucosal oxygen tension during seven hours of stress loading. The stress ulceration began to occur starting three hours after cold immersion in the control rats, and the deficit of energy metabolism was attributed to reduced oxidative phosphorylation from tissue hypoxia resulting from lowered blood flow and oxygen tension under stress. Cimetidine (4 mg/kg) maintained aerobic glycolysis, continued to produce high-energy phosphates and kept the energy charge unchanged in the gastric mucosa. In addition, PG E2-Me (100 micrograms/kg) showed similar, but less marked and shorter-lived effects on aerobic glycolysis and ATP production, whereas the energy charge of the adenosine pool decreased significantly from that produced by cimetidine. These results indicated that cimetidine significantly reduced energy requirements as compared with the control and PG E2 groups due to marked inhibition of gastric secretion and produced inhibition of mucosal ulceration by water immersion. On the other hand, increased energy requirements due to the rise of cytoprotective mucoprotein production and a resultant decrease of the energy charge were seen with PG E2 as compared with cimetidine.

Study of central neurotransmitters in stress-induced gastric ulceration in albino rats

1 Restraint when combined with cold (4 degrees C) consistently induces gastric ulceration in rats at 2 h. The cold-restraint ulcer (CRU) technique provides a suitable model for acute studies. 2 The peripheral mechanisms in CRU seem to be increased sympathetic and parasympathetic outflow since CRU was significantly reduced by prior spinal transection or vagotomy or by appropriate blocking agents. Since metiamide significantly reduced CRU, H2-histamine receptors are also involved. 3 Central catecholaminergic as well as cholinergic mechanisms seem to be responsible for the activation of peripheral sympathetic and parasympathetic outflow in CRU, since central administration of dibenamine, propranolol, 6-hydroxydopamine and atropine prevented the CRU. 4 Exogenous administration of putative neurotransmitters (adrenaline, noradrenaline and acetylcholine) into the cerebroventricular system produced gastric ulceration similar to CRU. However, dopamine, histamine and 5-hydroxytryptamine failed to induce gastric ulceration. 5 The results with intracerebroventricular adrenaline and acetylcholine indicate a central cholinergic link distal to adrenergic activation in the ulcerogenesis. 6 Intracerebroventricular adrenaline-induced gastric ulceration appears to be most akin to CRU. However, other central neurotransmitter mechanisms may also be involved.

Restraint ulcer: history, current research and future implications

A relatively new ulcerogenic procedure, supine restraint-cold, is described. This procedure is simple, effective andproduced a reliably high incidence of gastric glandular lesions in a variety of animal species. In some cases, these lesions penetrate the muscularis mucosa and as such may be called ulcers. They are responsive to known therapeutic agents (cimetidine, aluminum hydroxide). Drugs which modify autonomic activity (scopolamine, carbachol) affect the extent of supine restraint-cold induced gastric lesions. Animals which differ in open-field behaviors indicative of emotionality, show marked differences in gastric lesions induced by this procedure. It is suggested that the supine restraint-cold procedure meets the established criteria for a useful experimental ulcer model [25] and thus represents a viable research tool.

Effects of water-immersion stress on gastric secretion and mucosal blood flow in rats

The correlation between acid secretion and mucosal blood flow in the rat stomach during stress loading was determined to provide clues to the etiology of the gastric ulceration which thus occurs. The gastric acid output was increased remarkably by water-immersion stress at 23 degrees C, and this increase lasted while the stress was given, yet the mucosal blood flow did not show a corresponding increase. In rats stressed for 3 hr, ulcerative changes were observed in the glandular portion of the stomach. The stress-induced increase in acid output correlated well with the severity of erosions. Pretreatment of animals with atropine 10 microgram/kg, given subcutaneously, or vagotomy, inhibited the increase in acid output and also inhibited the ulcer formation caused by the stress: however, the mucosal blood flow in these animals decreased significantly. These results suggest that when there is an elevation of gastric acid secretion with no parallel increase in mucosal blood flow, gastric ulceration may occur under conditions of stress.

Cholinergic-mediated gastric mast cell degranulation with subsequent histamine H1-and H2-receptor activation in stress ulceration in rats

The effects of atropine, mepyramine, metiamide or NaHCO3 on gastric ulceration, gastric secretion and gastric mast cell degranulation were studied in stressed pylorus-occluded rats. The influence of dexamethasone pretreatment on stress ulcers in animals without pylorus occlusion (intact rats) was also examined. Stress produced a high glandular lesion incidence and ulcer index, and markedly lowered gastric secretion and glandular wall mast cell counts. Injected 0.5 h before stress, atropine, mepyramine or metiamide strongly antagonised ulceration. Atropine or metiamide, but not mepyramine, reduced gastric secretion. Only atropine prevented stress-induced mast cell changes. NaHCO3, given intragastrically before stress, did not prevent ulceration or mast cell degranulation despite complete neutralisation of gastric acid. Dexamethasone-induced gastric mucosal mast cell depletion could reduce stress ulceration. The findings show that stress degranulates stomach mast cells via a cholinergic pathway; released histamine from this source is largely responsbile for gastric ulceration through H1- and H2-receptor effects. Histamine H2-receptor-mediated gastric acid may play only a small contributory role in stress ulcers in rats. The antiulcer mechanisms of histamine H1- and H2-receptor blockade are discussed.

Histamine H1- and H2-receptor-mediated gastric microcirculatory effects in the aetiology of stress ulceration in the rat stomach

Stress produced severe mucosal ulcers, increased mucosal microcirculation and lowered mast cell counts in the glandular wall of rat stomachs. Mepyramine i.m. or metiamide i.p. effectively prevented both ulceration and microcirculatory changes but not stress-reduced mast cell counts.

Aspirin- and indomethacin-induced ulcers and their antagonism by antihistamines

Gastric ulceration produced by aspirin and indomethacin was compared in acutely stressed and non-stressed rats. We found a synergism between these anti-inflammatory agents and acute stress in the production of gastric ulcers. Even at relatively high doses, neither agent caused appreciable gastric damage in non-stressed rats, whereas moderate doses of both agents produced massive ulceration in stressed rats. The synergism appears unrelated to the effect of these agents on the pituitary-adrenal response. The size and regional distribution of ulcers produced by aspirin and indomethacin in stressed rats were comparable. However, the dose--response curves of the two drugs were markedly dissimilar. Furthermore, the ulceration produced by indomethacin was attenuated by both H1 and H2 histamine receptor antagonists, whereas ulceration produced by aspirin was attenuated only by an H2 antagonist. The results suggest that the ulcerogenic mechanism of indomethacin may differ from that of aspirin and add to the growing evidence on the importance of endogenous histamine in various forms of gastric ulceration.

Role of gastric motility in development of stress-induced gastric lesions of rats

Gastric motility of stressed rats was studied to determine its role in producing stress-induced gastric lesions. Restraint and water immersion resulted in an increase in gastric motility which consisted of an increase in frequency and amplitude of contractions and a rise in gastric tone. This increase reached maximal levels 2 to 4 hr after stress, and persisted thereafter. Formation of gastric lesions was markedly accelerated after occurrence of the increased gastric motility. In contrast, restraint alone neither produced such a vigorous increase in gastric motility, nor were the gastric lesions severe. A continuous infusion of papaverine during restraint and water immersion inhibited increase in frequency and amplitude of gastric contractions and prevented formation of gastric lesions. It is concluded that increased gastric motility is closely associated with marked formation of gastric lesions under conditions of restraint and water immersion stress and is probably a main cause for their vigorous formation, although formation of lesions occurs to a small degree without involvement of gastric motility.

Effects of cimetidine on stress ulcer and gastric acid secretion in the rat

Cimetidine at 25, 50, and 100 mg/kg significantly inhibited gastric acid secretion in rats with chronic gastric cannulas. Rats receiving either 50 or 100 mg/kg of cimetidine secreted significantly less gastric acid 3 hr after injection. Cimetidine failed to reduce the number or size of gastric lesions in rats exposed to the activity-stress procedure, but cimetidine at 100 mg/kg significantly reduced the number and size of gastric lesions in rats subjected to a supine restraint procedure.

Some observations on the gastric effects of phentolamine in rats

The effects of graded doses of phentolamine on gastric secretion, gastric emptying rate, gastric mucosal mucus content and gastric mucosal lesion incidence were studied in conscious rats 2 h after intramuscular administration. In pylorus-occluded rats, phentolamine (5, 10 or 20 mg/kg) produced dose-dependent decreases in the gastric secretory volume and total acid output. Similar doses of the drug also produced dose-dependent decreases in the gastric emptying rate in animals without pylorus occlusion (intact rats), but did not affect the gastric mucosal mucus content. The incidence of gastric mucosal lesions in pylorus-occluded or intact animals rose with increasing doses. The findings are discussed in the light of the possibility that phentolamine, in the dose range examined, possesses a sympathomimetic action which would underlie the gastric lesions observed.

A correlative study of the antiulcer effects of zinc sulphate in stressed rats

The effects on zinc sulphate pretreatment of rats on stress-induced gastric ulcers and on changes in mast cell counts were studied and correlated with changes in gastric mucosal microcirculation. The effects on zinc sulphate on blood pressure responses and on growth were also examined. Stress (2 h restraint at 4 degrees C) produced marked glandular mucosal ulceration, lowered the stomach wall mast cell counts and increased the microcirculatory blood volume in the superficial glandular mucosa. Zinc sulphate (22, 44 or 88 mg/kg; injected i.p. 48 h before stress) reversed all these changes in a dose-related manner. Blood pressure responses to i.v. acetylcholine, adrenaline or histamine were unaffected and growth of the rats as observed for 7 days after injection was not impaired. On the basis of these findings the mechanism of the antiulcer action of zinc sulphate is the following: inhibition of the stress-induced release of vasoactive agents from gastric mast cells and thus prevention of the subsequent microciculatory changes known to produce mucosal ulceration. Interference with vascular responses through direct blockade or toxicity is unlikely.

Does increased gastric mucus play a role in the ulcer-protecting effects of zinc sulphate?

Zinc sulphate pretreatment i.p. produces dose-related reductions in stess ulcer incidence in pylorus-occluded rats. The associated increases in gastric wall mucus, in stressed and nonstressed animals, suggest that a similar effect may contribute to its ulcer-reducing ability in man.

Effects of cimetidine, a histamine H2-receptor antagonist, on various experimental gastric and duodenal ulcers

The effects of cimetidine, a new histamine H2-receptor antagonist, on the development of experimental gastric and duodenal ulcers were studied. It was found that either by the oral, intraduodenal, or intraperitoneal route this agent had a marked inhibitory activity on stress-, aspirin-, indomethacin-, or histamine-induced gastric ulcers in rats and guinea pigs. The effects of cimetidine on stress-, aspirin-, and indomethacin-induced gastric ulcers were dose-dependent in many cases. Pylorus-ligation uclers, reserpine- or serotonin-induced gastric ulcers were little influenced by cimetidine. Duodenal ulcers induced by continuous infusion of carbachol-histamine were significantly inhibited by a simultaneous infusion of cimetidine. An analysis of gastric contents in pylorus-ligated rats after stressing indicated a decreased volume and acid output as the result of intraduodenal cimetidine treatment. In contrast, cimetidine exerted little influence on gastric secretion in rats treated with aspirin or in guinea pigs treated with histamine. Thus, the mechanism of action of cimetidine in preventing gastric or duodenal ulcers is likely to occur by suppression of gastric secretory function in a duodenal ulcer model but by suppression of other unknown ulcerogenic factors in gastric ulcer models.

The effects of zinc sulphate on vagal-induced mast cell changes and ulcers in the rat stomach

The effects of zinc sulphate pretreatment on the formation of gastric ulcers, changes in intragastric pressure and changes in the gastric mucosal mast cell count induced by electrical vagal stimulation were studied in anaesthetized rats. Vagal stimulation produced a high gastric glandular ulcer incidence and ulcer index, increased the intragastric pressure, and reduced the number of granulated mast cells in the gastric mucosa and submucosa. Pretreatment with zinc sulphate (22, 44 ot 88 mg/kg), injected i.p. 48 h beforehand, reversed the changes in these parameters in a dose-related manner. These observations suggest that the inhibitory effects of zinc sulphate on mucosal mast cell degranulation may account for its ability to antagonise vagal-induced gastric glandular ulceration. The mechanisms involved in the aetiology of this type of gastric ulcer are discussed in the light of these results.

A new model of stress ulcer in the rat with pylorus ligation and its pathogenesis

Water-immersion stress for 7, 14, or 20 hr consistently induced linear or punctate stress ulcers (mucosal erosions) in the corpus of the stomach in intact rats. When the pylorus of the stomach had been ligated prior to stressing, the stress ulcers changed their morphological feature (mainly punctate and in one place elongated) and location (both in corpus and antrum). Histologically, the stress ulcer developed in the proximal antrum of pylorus ligated rats and penetrated into the muscularis mucosa. Sodium bicarbonate, chlorpromazine, hexamethonium, atropine, metiamide, and bilateral vagotomy markedly inhibited the stress ulcers which developed in the pylorus-ligated rats. Phentolamine and propranolol hardly affected the development of stress ulcers. Amylopectine evoked a new type of stress ulcer in the corpus when it was given to the pylorus-ligated rats.

Effects of zinc chloride on gastric secretion and ulcer formation in pylorus-occluded rats

The effects of 10-day pretreatment with i.p. injections of zinc chloride, 16 mg/kg, on gastric secretion and on gastric ulceration induced by stress or by acid accumulation were examined in pylorus-occluded rats. Zinc chloride pretreatment significantly reduced the volume of gastric secretion and the total acid output as well as the incidence of gastric ulcers induced either by stress or by acid accumulation. The findings support the idea zinc compounds may be useful in the treatment of gastric ulcers.

Intragastric NaHCO3 perfusion and vagal-induced ulcer formation in the rat stomach

The effects of electrical vagal stimulation on gastric acid output and ulcer formation were studied in rats intragastrically perfused with saline or NaHCO3 solutions. Vagal stimulation produced a 100% incidence of glandular lesions and a significant increase in total acid output in saline-perfused stomachs. Antacid perfusion failed to prevent ulcer formation despite complete neutralization of the increased acid output. It is considered that vagal-induced gastric glandular lesions are not acid dependent.

Acute gastric ulcer formation in response to electrical vagal stimulation in rats

Intermittent electrical stimulation of the left cervical vagus increased intragastric pressure and induced a 100% incidence of haemorrhagic ulcers in the glandular mucosa of rat stomachs. Atropine pretreatment of sub-diaphragmatic vagotomy prevented these effects. The findings substantiate the idea that stress-induced glandular ulcers result from vagal-mediated increased gastric contractions.

The effects of metiamide on gastric secretion and stress ulceration in rats

The effects of metiamide, a histamine H2 blocker, on gastric secretion and ulcer formation in stressed pylorus-occluded rats were investigated. Metiamide, like atropine, significantly reduced the volume of gastric secretion and total acid output in unrestrained pylorus-occluded rats. Both drugs produced greater decreases in the volumes of gastric secretion in stressed rats than in their corresponding unrestrained groups. Stress itself reduced both parameters. Metiamide, like atropine, significantly reduced the incidence of gastric stress ulcers. When given together these two drugs did not provide greater protection. The results obtained with metiamide indicate that histamine plays a role in basal gastric secretion and in the pathogenesis of stress ulcers. As no correlation between gastric acid secretion and ulcer formation was demonstrated in this study, it is suggested that H2 receptors may also be involved in gastric motility. However, the possibility that metiamide could exert its ulcer-protecting effects through other mechanisms cannot yet be excluded.

Effects of stress and of autonomic blockers on gastric mucosal microcirculation in rats

Changes in gastric mucosal microcirculation in rats were studied by using the method of intra-aortic injection of India ink, followed by microdissection of the mucosa. Acute stress, induced by restraint and exposure to cold for 2 hr, caused marked and significant vasodilatation in the gastric mucosa. This vasodilatation was prevented by pretreatment with atropine or chlorpromazine, but not by alpha- or theta-adrenoceptor blocking agents. Phentolamine caused significant vasoconstriction in the gastric mucosa of non-stressed rats, but when animals were stressed phentolamine induced a greater vasodilatation than was obtained with stress alone. These observations provide added support for the hypothesis that stress induces vagal overactivity, probably of central origin. The resulting strong contractions of the gastric wall, and compression of the intramural vessels, are probably responsible for degeneration of the mucosal cells leading to the formation of stress-induced ulcers in the rat.