Effects of adrenergic blocking agents on gastric secretion and stress-induced gastric ulcer in rats

Subacute toxicity study of patulin in the rat: effects on the kidney and the gastro-intestinal tract

Female and male Wistar rats were given drinking-water containing patulin at concentrations of 0, 24, 84 or 295 mg/litre citrate buffer (1 mM) for 4 wk. Compared with the controls, there were decreases in food and liquid intake by rats given the mid and high doses of patulin and the body weights of rats in the high-dose group were also decreased. The creatinine clearance in the high-dose group was lowered, although morphological glomerular damage was not observed. In the high-dose group, fundic ulcers in the stomach and enlargement and activation of the pancreatico-duodenal lymph nodes were noticed, while villous hyperaemia in the duodenum was observed in the mid- and high-dose groups. From the present data it can be concluded that high doses of patulin, administered via the drinking-water, caused effects on the kidney and gastro-intestinal tract. Since no changes in the relative weight or histological appearance of the adrenal glands were observed, it is suggested that the fundic ulcers in the stomach were caused by a direct effect of patulin and not indirectly (i.e. by stress).

Histopathological studies of experimental marine toxin poisoning. II. The acute effects of maitotoxin on the stomach, heart and lymphoid tissues in mice and rats

Maitotoxin, one of the causative agents of ciguatera isolated from marine dinoflagellate, Gambierdiscus toxicus, induced severe pathomorphological changes in the stomach, heart and lymphoid tissues in mice and rats. Multiple erosions were observed in gastric mucosa accompanied by a marked increase in total calcium content 24 hr after i.p. injection of 200 or 400 ng/kg of maitotoxin. In contrast, there was no close temporal association between the accumulation of calcium and the morphological appearance of dead cells in the heart and thymus. Within 30 min of administration of 200 or 400 ng/kg of maitotoxin, a marked swelling was seen in the endothelial lining cells of blood capillaries between cardiac muscle fibers, followed by the cell death of the fibers. Injection of maitotoxin at a dose of 200 ng/kg or higher also resulted in necrosis of lymphocytes in the cortex of the thymus at 4 hr and in the medulla at 8 hr.

Gastric mucosal defence mechanism during stress of pyloric obstruction in albino rats

1. The integrity of the gastric mucosa and its ability to secrete mucus are believed to be essential for protection of gastric mucosa against ulceration induced by aggressive factors active in any stress situation. This study involves a three-compartmental analysis of gastric mucosal barrier in pylorus-ligated albino rats. 2. Quantitative analyses of histologically identifiable gastric mucosal epithelial neutral glycoproteins and gastric adherent mucus from oxyntic and pyloric gland areas, and components of non-dialysable mucosubstances in gastric secretion were made under stress of pyloric obstruction for 4, 8, and 16 h durations. Epithelial mucin was identified by periodic acid-Schiff (PAS) staining technique and assessed from the ratio of gastric mucosal thickness to the depth of PAS positive materials in it. The remaining visible mucus adhered to the gastric mucosa was estimated by Alcian blue binding technique. The results were compared with that of identical control groups. 3. A significant reduction in mucosal epithelial PAS positive materials after 8 or 16 h of pylorus ligation was observed. 4. The Alcian blue binding capacity of the pyloric gland area was increased significantly after 4 h of pylorus ligation, while after 8 or 16 h it was reduced in both oxyntic and pyloric gland areas. 5. Significant reductions in the rate of gastric secretion and volume, as well as concentration of the components of non-dialysable mucosubstances, were observed, indicating decreased synthesis of mucus glycoproteins. 6. Disruption of the mucosal barrier may have occurred due to decreased mucus synthesis and acid-pepsin accumulation; both could be due to stress associated with gastric distension. 7. The present findings confirm the role of mucus in protecting the underlying gastric epithelium during stress. The adherent mucus offers a first line of defence and epithelial mucus a second line of defence.

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.

Enhancement by intracerebroventricular thyrotropin-releasing hormone of indomethacin-induced gastric lesions in the rat

Effects of the intracerebroventricular thyrotropin-releasing hormone (TRH) on gastric mucosa were studied in rats. TRH (3 and 10 micrograms rat-1 i.c.v.) produced slight gastric lesions and also aggravated indomethacin-, aspirin- or 5-hydroxytryptamine (5-HT)-induced gastric lesions, while restraint and cold stress-induced lesions were not influenced by TRH. Bethanechol used at a dose sufficient to produce acid secretion did not influence the gastric mucosa in intact or indomethacin-treated rats. Enhancement of indomethacin-induced gastric lesions by TRH was not inhibited to any significant degree by atropine 0.1 mg kg-1 s.c., which prevented TRH-induced gastric acid secretion, but tended to be inhibited by phentolamine, 2.5 mg kg-1 i.p. It is concluded that the enhancement by TRH of indomethacin-induced gastric lesions is due to a combination of the central and peripheral actions of the ulcerogenic agents.

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.

Autonomic drug effects and gastric secretion in a new experimental model of stress ulcers in rats

A psychological procedure which does not involve the application of physical stimulation was used to produce gastric ulcers experimentally. Ulceration was induced in rats by exposing the animals to the aggressive attacks of rats treated with 6-hydroxy-dopamine (6-OHDA). Gastric secretion and the effects of autonomic drugs on ulcer formation were investigated. Atropine methylbromide did not significantly inhibit the occurrence of erosions. Phentolamine or hexamethonium bromide significantly inhibited the production of erosions, and combined administration of an anticholinergic agents and alpha-blocking agent led to a complete inhibition, with no notable behavioral change. In case of pylorus ligation, gastric secretion during exposure to attack of 6-OHDA-treated rats was significantly less than that in the controls. We suggest that the sympathetic nervous system plays an important role in the production of gastric erosions, as induced by the methods reported in this study.

Polyamine inhibition of gastric ulceration and secretion in rats

The effect of polyamines on gastric ulceration and secretion in rats was studied. Stress-induced gastric ulceration and ulceration in pylorus-ligated rats were inhibited by subcutaneous or oral administration of spermine; spermidine's inhibitory effect was somewhat less. Histamine-induced ulceration was also inhibited by the subcutaneous injection of spermine. In addition, the daily oral administration of spermine for 10 days was therapeutic against an acetic acid-induced ulcer (chronic ulcer). Gastric secretion in pylorus-ligated rats and in rats with fistulae and stimulated by histamine injection was decreased by the subcutaneous injection of spermine.

Gastric antral ulcers produced by the combined administration of indomethacin with 2-deoxy-D-glucose in the rat

The influence of 2-deoxy-D-glucose (2DG) on indomethacin ulcers was studied in rats. 2DG (200 mg/kg i.v.) produced large round ulcers in the lesser curvature of the antrum and aggravated lesions of the corpus 6 h after treatments in indomethacin (40 mg/kg i.p.)-treated rats. Insulin (5 units/kg i.v.) also produced gastric antral ulcers similarly to 2DG. Antral ulcers were revealed rather clearly 48 h after the administration of indomethacin and 2DG when the corpus lesion index was reduced. 2DG or insulin had only a slight influence on the severity of other experimental gastric ulcers. Peripheral gastric secretagogues, bethanechol (1 mg/kg s.c. X 2) or histamine (10 mg/kg s.c. X 2) did not produce antral ulcers at the gastric secretory dose in the indomethacin-treated rats. High doses of atropine (1.0 and 10 mg/kg s.c.) prevented gastric antral ulcers. The combined administration of indomethacin with 2DG produced gastric antral ulcers similar to human gastric ulcers in rats. The combination of gastric acid secretion, vagus nerve stimulation and some other factors may be involved in gastric antral ulcers produced in rats.

The effect of alpha- and beta-receptor blocking agents on gastric acid secretion in guinea-pigs

The effects of alpha- and beta-receptor blocking agents on gastric acid secretion were tested on 95 female guinea-pigs. Alpha blockade insignificantly inhibited the gastric acid secretion in the unstimulated animals, whereas in those stimulated with histamine, significant reduction was seen. Beta blockade had no influence on gastric secretion in the unstimulated animals but significantly enhanced the histamine-stimulated secretion of acid.

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.

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.

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.

Effects of metiamide and propranolol on gastric secretion in anesthetized dogs

The effects of metiamide, a histamine H2-receptor antagonist, and propranolol, a beta-adrenergic blocking agent, on gastric secretion were studied in anesthetized dogs. Metiamide, 1.45 mg/kg i.v., markedly inhibited the gastric secretion induced by a continuous i.v. infusion of tetragastrin (8 microng/kg-hr), histamine dihydrochloride (160 microng/kg-hr), or methacholine bromide (100 microng/kg-hr). Propranolol 0.5 or 1.0 mg/kg i.v. produced a significant potentiation of tetragastrin-induced gastric secretion but no influence of the secretion induced by methacholine. Propranolol at 5 or 10 mg/kg i.v. produced a slight reduction of the tetragastrin-induced secretion and a significant reduction of methacholine-induced secretion. Histamine-induced gastric secretion was not affected by propranolol at either 1 and 10 mg/kg i.v. These findings lend support to the hypothesis that interactions among histamine, gastrin and acetylcholine receptors do occur though the degree would not be the same in all directions.

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 propranolol on gastric secretion in albino rats

1 Effects of graded doses of propranolol have been studied on gastric secretion and gastric ulcers in pylorus-ligated rats.2 A dose-dependent action of propranolol was observed; small doses increased total volume, acid output and pepsin secretion along with an increase in the incidence of ulcers but high doses were inhibitory.

Can the actions of adrenoceptor agonists and antagonists on pentagastrin-induced gastric secretion be due to their effects of histamine formation?

1 The effects of some adrenoceptor agonists and antagonists which have been reported to affect histamine formation in leucocytes (Assem & Feigenbaum, 1972) have been investigated on gastric secretion in conscious dogs with Heidenhain pouches.2 Submaximal secretion in response to pentagastrin was enhanced by propranolol (0.1-1.0 mg/kg i.v.) and phenylephrine (1.0 mug kg(-1) min(-1) i.v. for 20 min), which increase histamine formation, and was decreased by phentolamine (2 mg/kg i.v.) and isoprenaline (0.05-0.2 mug kg(-1) min(-1) i.v. for 30 min), which decrease histamine formation. Practolol (2 mg/kg i.v.), which has no effect on histamine formation, had no effect on secretion.3 Acid secretion in response to histamine was either unaffected or affected in the opposite direction by these drugs.4 The effects of the drugs on pentagastrin-induced secretion were not secondary to changes in mucosal blood flow (radioactive aniline clearance).5 The results are consistent with the hypothesis that acid secretion in response to pentagastrin involves the formation of endogenous histamine.

Effect of propranolol on gastric acid secretion in rats

The effect of propranolol, a beta-adrenoceptor blocking agent, has been investigated on gastric acid secretion in pylorus and cardiac-ligated rats. Compared to the control group, propranolol significantly diminished the gastric acid secretion, and inhibited the formation of gastric ulceration.