Mechanisms of antisecretory action of intragastric FPL-52694: a mast cell stabilizer in anesthetized rats

Mechanisms of antisecretory action of intragastric FPL-52694, a mast cell stabilizer, were investigated in anesthetized rats. In Schild's rat preparation, intravenous FPL-52694 (10 mg/kg) significantly suppressed acid secretion in response to only tetragastrin (20 micrograms/kg, i.v.) (42.1 +/- 19.4%), while intragastric application of FPL-52694 (100 mg/kg) for 30 min produced a marked, unequivocal inhibition (over 70%) in acid secretory responses to histamine (1 mg/kg, i.v.) and carbachol (2.5 micrograms/kg, i.v.) as well as tetragastrin. The inhibitory effect of intragastric FPL-52694 was confirmed in the lumen-perfused rats, where acid secretion (24-25 mumol/10 min) induced by intravenous infusion of histamine (8 mg/kg/h) was abolished for 1 h after exposure of the stomach for 30 min to this agent. Inhibition of histamine-stimulated acid secretion by intragastric FPL-52694 was much greater and lasted longer (2 h) as compared with xylocaine (4% solution), but significantly mitigated by pretreatment of the rats with subcutaneous administration of indomethacin (3 mg/kg). Furthermore, application of FPL-52694 but not of xylocaine to the stomach caused a reduction of transmucosal potential difference, an increase of luminal appearance of HCO-3 (1-2 mumol/10 min), and an enhancement of H+ back-diffusion, although no damage was appreciated in the mucosa. These results suggest that antisecretory action of intragastric FPL-52694 may involve local mechanisms such as neutralization of acid with HCO-3, a loss of acid due to H+ back-diffusion, and inhibition of acid production mediated by endogenous prostaglandins, but is not related to the local anesthetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of luminal Ca2+ on normal and damaged gastric mucosa in the rat

Influence of luminal Ca2+ on the integrity of normal mucosa and recovery of damaged mucosa in anesthetized rat stomachs was studied using a perfusion system. Changes in the mucosal integrity were monitored by measuring transmucosal potential difference (PD) and luminal pH. EDTA, a Ca2+ chelator, dose-dependently reduced PD and increased luminal pH. Five mM Ca2+ (CaCl2) alone produced no changes in either PD and luminal pH, but the PD which was reduced by 250 mM EDTA was significantly recovered. Ethanol or NaCl concentration-dependently reduced PD, but gradually reverted to baseline levels. While 5 mM Ca2+ or 5 mM EDTA did not influence the reduction in PD with 50% ethanol and 1 M NaCl, these agents either enhanced or delayed the recovery processes in reduced PD, respectively. Five mM Ca2+ enhanced the recovery of PD which was reduced by 50% ethanol plus 5 mM EDTA. Gastric damage induced by 50% ethanol plus 5 mM EDTA was much more severe than that induced by 50% ethanol alone or 50% ethanol plus 5 mM Ca2+. Both 50% ethanol and 1 M NaCl significantly increased Ca2+ contents in the gastric lumen. Luminal Ca2+ appears to play an important role in maintaining mucosal integrity, under normal physiological conditions, and in accelerating the recovery process of damaged mucosa in rat stomachs.

Characterization of FPL-52694 [5-(2-hydroxypropoxyl)-8-propyl-4-oxo-4H-benzopyran-2-carboxylic acid Na] on histamine release from rat peritoneal mast cells induced by antigen, compound 48/80 and A 23187

We studied the in vitro effects of FPL-52694 [5-(2-hydroxypropoxyl)-8-propyl-4-oxo-4H-benzopyran-2-carboxylic acid Na] on histamine release from rat peritoneal mast cells. These cells exposed to ascaris antigen, compound 48/80 or the ionophore A 23187 concentration-dependently released histamine. About a 30-40% histamine release was obtained by 1 X 10(-4) g/ml of antigen, 1 X 10(-7) g/ml of compound 48/80 and A 23187. FPL-52694 (10(-9)-10(-4) g/ml) concentration-dependently inhibited the histamine release from mast cells in response to antigen (1 X 10(-4) g/ml) and compound 48/80 (1 X 10(-7) g/ml), but only slightly inhibited the histamine release induced by A 23187 (1 X 10(-7) g/ml). Similar results were obtained with disodium cromoglycate (DSCG), in the same dose ranges. However, the inhibitory activity of FPL-52694 on histamine release by antigen and compound 48/80 was approximately 10 times more potent than that of DSCG at certain concentrations. Tachyphylaxis was observed when these two agents were preincubated with mast cells for 10 min. These results show FPL-52694 to be a novel mast cell stabilizer.

Effects of prolonged treatment with compound 48/80 on the gastric mucosa and mast cells in the rat

Effects of prolonged administration of compound 48/80 (48/80) on the gastric mucosa, serotonin and histamine levels in serum, and mast cells of rats were studied. Daily administration of 48/80 (0.75 mg/kg, i.p.) for 2 or 4 days produced widespread gastric lesions. Further administration of the agent for up to 12 days did not aggravate the lesions which had developed in the early period of administration of the drug. There were only a few visible lesions and numerous healed ones. Almost the same phenomenon was observed with the daily administration of serotonin plus histamine (10 mg/kg each, i.p.) for 2 to 12 days. While 48/80 given for 2 or 4 days increased serotonin and histamine levels in serum, it induced no appreciable increase of these amines after 8 or 12 days of treatment. Serotonin and histamine levels in peritoneal mast cells significantly decreased after the treatment with 48/80 over a 4 day period. The decrease in gastric lesions after prolonged treatment with 48/80 is due to both the depletion of serotonin and histamine from mast cells and an increased resistance of the gastric mucosa with healed lesions.

Effects of various agents on prednisolone-induced gastric lesions in rats

We studied the effects of various agents on prednisolone-induced gastric lesions in rats. Gastric lesions were produced by subcutaneous administration of 50 mg/kg of prednisolone once daily for 4 days to non-fasted rats. Daily oral administration of antipeptic, antisecretory agents and 16-dmPGE2 significantly inhibited the lesions. Antacids and PGI2 had little or not effect. These results suggest that the concomitant use of the above agents with steroid therapy to provide protection of the gastric mucosa warrants further attention.

[Effects of gefarnate on acute gastric lesions in rats]

The effects of gefarnate on several acute gastric lesions were studied in rats. Gefarnate, given at either 100 approximately 1000 mg/kg orally or intraduodenally, dose-dependently inhibited the formation of gastric lesions induced by HCl-ethanol, HCl-taurocholate and aspirin. Cimetidine, given at 30 approximately 100 mg/kg as a reference drug, also significantly inhibited both HCl-ethanol and aspirin-induced lesions. The present study suggests that gefarnate, as well as cimetidine, is useful for the treatment of acute gastric lesions in man.

Effects of 16,16-dimethyl prostaglandin E2 on ethanol-induced and aspirin-induced gastric damage in the rat. Scanning electron microscopic study

Ethanol and aspirin were administered orally to fasted rats and the effects of 16,16-dimethyl prostaglandin E2 (given orally as a pretreatment) were studied using scanning electron microscopy. Gastric secretory studies (pylorus ligation for 2 h) showed that 3 and 30 micrograms/kg of 16,16-dimethyl prostaglandin E2 were nonantisecretory doses and that 100 micrograms/kg was an antisecretory dose. 16,16-Dimethyl prostaglandin E2, given orally at 3-100 micrograms/Kg, induced no appreciable changes in the gastric surface epithelial cells. Oral administration of 1 ml of 50% ethanol invariably induced, within 10 min, extensive exfoliation of surface epithelial cells throughout the corpus and antrum and exposed the lamina propria. 16,16-Dimethyl prostaglandin E2, given orally at 3, 30, and 100 micrograms/kg 30 min before ethanol treatment, had no protective effect. Aspirin, given orally at 30 or 100 mg/kg, also damaged the surface epithelium of both the corpus and the antrum within 10 min. This damage ranged from apical cellular erosions to widespread exposure of the lamina propria. 16,16-Dimethyl prostaglandin E2, given orally at 3 or 30 micrograms/kg 30 min before aspirin treatment, significantly inhibited the gastric damage induced by both 30 and 100 mg/kg of aspirin. The inhibition of damage index was about 50%-60% at either 30 or 100 micrograms/kg of 16,16-dimethyl prostaglandin E2. The mechanism of the protection seen with 16,16-dimethyl prostaglandin E2 remains to be determined.

Effects of FPL-52694, a new mast cell stabilizer, on gastric secretion and various acute gastric lesions in rats

Oral FPL-52694 [5-(2-hydroxypropoxy)-8-propyl-4-oxo-4H-1-benzopyran-2-carboxylic acid Na], a new mast cell stabilizer, dose-dependently inhibited gastric acid secretion but increased the volume and pepsin output in pylorus-ligated rats. Intraduodenal FPL-52694 significantly inhibited all of the volume, acidity, acid output and pepsin output. Concerning the acidity, oral administration of the agent showed much more potent inhibition than intraduodenal administration. Oral FPL-52694 markedly inhibited the development of pylorus-ligated ulcers, water-immersion stress- and aspirin-induced gastric erosions and moderately inhibited the formation of reserpine-induced gastric erosions in rats. Intraduodenal FPL-52694 also inhibited pylorus-ligated ulcers whereas it had no effect on aspirin-induced gastric erosions. Histamine-induced gastric erosions were not affected by oral FPL-52694. These effects of FPL-52694 were almost the same as those of cimetidine, except that cimetidine tended to inhibit histamine-induced gastric erosions. Although the precise mechanism of action of FPL-52694 remains unknown, oral FPL-52694 appears to be a promising agent for the treatment of peptic ulcers.

Comparative study of hydrogen and aminopyrine clearance methods for determination of gastric mucosal blood flow in dogs

Effects of pentagastrin, histamine, PGI2, and vasopressin on gastric mucosal blood flow (GMBF) in innervated stomaches of anesthetized dogs were measured by means of the hydrogen clearance method, using a contact electrode. The results were compared with findings obtained with the aminopyrine (AP) clearance method in Heidenhain pouch preparations. Pentagastrin at 2 and 8 micrograms/kg/hr had no effects on GMBF, as measured by the hydrogen clearance method, but there was a marked increase in GMBF when the AP clearance method was used. Histamine at 40 or 160 micrograms/kg/hr tended to reduce or significantly reduced GMBF when measured with the hydrogen clearance method, but there was a significant increase in GMBF with the AP clearance method. Both PGI2 (3 or 30 micrograms/kg/hr) and vasopressin (0.06 or 0.25 units/kg/hr) reduced GMBF as determined by both methods. These results indicate that the hydrogen clearance method is advantageous for detecting regional GMBF but is disadvantageous when attempting to detect the effects of agents which increase GMBF.

Time variation of radon daughters concentration in snowfall

Time variation of radon daughters concentration in snowfall was measured continuously. The relations of radon daughters concentration in snowfall to the precipitation and to atmospheric radon daughters concentration were investigated. It has become clear that when precipitation is small, radon daughters concentration in snowfall is distributed in a wide range, and that the quantity of radon daughters brought to ground surface by snowfall is proportional to precipitation. Washout effect of the snowfall on atmospheric radon daughters was also investigated.

Effects of a proton pump inhibitor, omeprazole, on gastric secretion and gastric and duodenal ulcers or erosions in rats

The effects of omeprazole, a proton pump inhibitor, on gastric secretion and gastric or duodenal ulcers or erosions in rats were studied. Omeprazole, given intraduodenally, dose-dependently inhibited the gastric secretion (volume, acid and pepsin output) of pylorus-ligated rats. The antisecretory activity of omeprazole at 100 mg/kg persisted for 14 hr after treatment. Acutely induced gastric ulcers or erosions such as Shay ulcers, water-immersion stress-, indomethacin-, aspirin-, or prednisolone-induced erosions were all markedly inhibited by oral or intraduodenal administration of 10-100 mg/kg of omeprazole. The development of duodenal ulcers and gastric erosions caused by mepirizole was also potently inhibited by omeprazole at 3-10 mg/kg given orally. Repeated administration of omeprazole, 200 mg/kg/day in two divided doses for 14 days, significantly accelerated the spontaneous healing of acetic acid-induced gastric ulcers. The mechanism by which omeprazole inhibits the development of acute ulcers and accelerates healing of preexisting ulcers appears to be mainly due to its potent and long-lasting antisecretory activity. The antisecretory and antiulcer activities of omeprazole are equal to or exceed those of cimetidine, both in the maximum inhibitory response and ED50 values.

Role of lymphoid nodules in pathogenesis of indomethacin-induced gastric lesions in dogs

Pathogenesis of indomethacin-induced gastric lesions in beagles was studied morphologically. While a single oral administration of indomethacin (20 mg/kg) did not induce visible lesions in the stomach of male beagles, repeated administration once daily for 5 or 10 days induced gastric erosions or ulcers, mainly in the antrum. When this compound was given once or repeatedly, histological examination showed that the total number of lymphoid nodules both in the fundus and antrum tended to increase or significantly increased. The number of large nodules (over 350 micron in diameter) was significantly increased, particularly in the antrum. Some of these enlarged nodules seen at the surface of the mucosa showed damage at the luminal area, and the lesions were microscopically visible. Indomethacin is known to disrupt the gastric mucosal barrier in dogs, leading to increased back-diffusion of acid. Our findings and those of others suggest that indomethacin may induce lesions in specific portions of the dog stomach, initiated by enlargement of lymphoid nodules followed by damage to some of these nodules, probably due to a corrosive effect of gastric juice through the disrupted mucosal barrier.

Factors related to gastric hypersecretion during pregnancy and lactation in rats

We attempted to elucidate the factors involved in gastric hypersecretion of rats during pregnancy and lactation. Acid secretion in pylorus-ligated and vagally denervated fistula rats stimulated with histamine, tetragastrin, and methacholine increased from midterm pregnancy and persisted during lactation. Pepsin secretion remained unaltered during pregnancy but increased during lactation. Vagal denervation itself abolished this hypersecretion. In late pregnancy, a delayed appearance of maximal acid response to histamine was apparent, as compared to nonpregnant rats, and was abolished by aminoguanidine treatment. There was a delay in the maximal response to tetragastrin but not to methacholine. Serum histamine concentrations were 3-4 times higher in late pregnancy, as compared to nonpregnant, lactating and nonlactating rats. Gastric DNA and protein concentrations were significantly increased in lactating rats with concomitant elevation of food intake and serum gastrin levels. Those changes disappeared in nonlactating rats, and gastric secretion was much the same in the nonpregnant rats. These results indicate that acid hypersecretion during pregnancy was exclusively associated with vagal innervation plus high serum histamine levels, while acid and pepsin hypersecretion in lactating rats were associated with vagal innervation plus hyperplastic gastric mucosa and high serum gastrin levels.

Gastric secretory conditions and plasma gastrin levels in rats after prolonged treatment with cimetidine

Effects of 4 weeks of treatment with oral cimetidine, 100 mg/kg twice daily, on gastric secretion and plasma gastrin levels were studied in rats. Pylorus ligation-induced and pentagastrin-stimulated gastric secretions were little changed at days 1, 3, and 10 after cessation of cimetidine treatment as compared to the controls. Histamine-stimulated acid secretion was significantly higher in the cimetidine-treated group than in the controls at day 3 after cimetidine treatment but was unchanged at days 1 and 10. A single oral administration of cimetidine at 100 mg/kg significantly increased plasma gastrin levels 4 hr after the treatment in refed rats but not at 2 and 8 hr later. Plasma gastrin levels significantly decreased at days 3 and 10 after cessation of cimetidine treatment as compared to the controls. Thus, while prolonged treatment with cimetidine induces a transient increase in response of parietal cells to histamine and a reduction of food-stimulated gastrin release, it does not seem to induce other appreciable changes in gastric secretion.

Role of luminal alkalinization in repair process of ethanol-induced mucosal damage in rat stomach

Changes in transmucosal potential difference (PD) and luminal pH after intragastric application of ethanol were simultaneously determined in stomachs of anesthetized rats. When the stomachs were exposed to 5-50% ethanol for 10 min, the PD was abruptly reduced and gradually returned to the basal levels, while the luminal pH gradually increased; these responses were concentration-dependent. The reduction of PD with 10% ethanol rapidly returned to the basal level without any changes in luminal pH. The PD after 50% ethanol gradually returned to the basal level in 3 hr, during which time luminal pH was kept at around 6. In cimetidine plus atropine-treated rats, considerably greater amounts of HCO3- were evident in the perfusate. The surface mucosal cells damaged by 50% ethanol recovered in parallel with the recovery of PD. When the stomach pH was maintained at a low level by an intravenous infusion of histamine or intragastric perfusion of 0.01 N HCl, the PD remained at a reduced level and the mucosal damage was aggravated. The perfusion of 0.01 N NaHCO3 kept the luminal pH at around 8-9, but it did not affect the recovery process of PD after 50% ethanol. These results suggest that application of ethanol induces luminal alkalinization, probably by HCO3- diffusion through the broken barrier, which in turn plays a role in the recovery from damage.

Effects of an antiulcer drug, sucralfate (a basic aluminum salt of sulfated disaccharide), on experimental gastric lesions and gastric secretion in rats

The effects of oral sucralfate, a basic aluminum salt of sulfated disaccharide, on various experimental gastric lesions and on gastric secretion were studied in rats. Sucralfate at 300 mg/kg potently inhibited the development of Shay ulcers and indomethacin- and aspirin-induced erosions. The drug at 1000 mg/kg also potently inhibited histamine-induced erosions. Water-immersion stress-induced erosions were inhibited with 1000 mg/kg of the drug, but the degree of inhibition was weaker than that seen in other types of erosion formation. Sucralfate at 1000 mg/kg given twice daily for 14 days significantly accelerated the spontaneous healing of acetic acid-induced ulcers. Sucralfate at over 300 mg/kg tended to increase the volume of gastric juice but had an insignificant effect on acid and pepsin output of pylorus-ligated rats. As a whole, the effects of sucralfate on experimental gastric lesions appear to be much more potent than Maalox, propantheline bromide, and cimetidine. The mechanism of action of sucralfate remains to be determined.

Species and strain differences in mepirizole-induced duodenal and gastric lesions

Species and strain differences in mepirizole-induced duodenal and gastric lesions were studied. Mepirizole at 200 mg/kg given orally induced deep duodenal ulcers and gastric erosions in nonfasted Sprague-Dawley, Fisher, Wistar, and Donryu rats at an incidence of over 75%. Mepirizole at 300 mg/kg given orally also induced penetrating duodenal ulcers in nonfasted rabbits at an incidence of 50%. There was little or no damage to the duodenum and stomach in mice and dogs given 200-300 mg/kg of mepirizole orally or subcutaneously. The stomachs of fasted guinea pigs given 200 mg/kg of mepirizole had superficial erosions at a high incidence (93.3%). Mepirizole at 200 mg/kg given intraduodenally significantly reduced the volume of gastric juice but increased the acidity and pepsin activity in both pylorus-ligated and acute fistula rats. In chronic fistula rabbits, however, the agent at 200 mg/kg given orally reduced the volume and acidity, but increased the pepsin activity. The mechanism of duodenal ulceration by mepirizole differs slightly in rats and rabbits.

[Effects of SM powder, a combined herbal preparation for stomach diseases, on gastric secretion and acute gastro-duodenal lesions in rats]

One gram of SM powder consists of 167.8 mg of Coptidis Rhizoma Pulveratum, 250 mg of Cinnamomi Cortex Pulveratus, 67.1 mg of Foeniculi Fractus Pulveratus, 33.6 mg of Caryophylli FLos Pulveratus, 82.1 mg of Zingiberis Rhizoma Pulveratus, 3.4 mg of Zanthoxyli Fructus Pulveratus, and 396 mg of Glycyrrhizae Radix Pulberata. SM powder (2 g/kg, i.d.) significantly inhibited gastric secretion in pylorus-ligated rats and the development of Shay ulcers and indomethacin-induced gastric lesions. The mechanism of the anti-lesion activity of SM powder appears to be due to its antisecretory effect. SM powder also markedly inhibited ethanol- or NaOH-induced gastric lesions at doses (30 or 100 mg/kg) which had little effect on gastric secretion. SM powder appears to have a cytoprotective activity which is unrelated to endogenous prostaglandins. However, SM powder had no effect on water-immersion stress- or aspirin-induced gastric lesions and mepirizole-induced duodenal ulcers. Gentiana Radix Pulverata, used as a reference stomatic, had also an antisecretory effect and anti-lesion activity on Shay ulcers, aspirin-, ethanol- and NaOH-induced gastric lesions. However, it had no effect on water-immersion stress- or indomethacin-induced gastric lesions and mepirizole-induced duodenal ulcers.

Acid back-diffusion and mucosal H+ handling in the rat stomach under normal and stress-induced conditions

We determined acid back-diffusion and pepsin output simultaneously in vagotomized rats after instillation of HCl into the stomach under normal and stress-induced conditions. With exposure to 6 ml of 100 mM HCl, spontaneous acid back-diffusion increased with the duration of the experiment under both conditions, and the magnitude of the acid back-diffusion was decreased significantly by stress. There was no change in the output of pepsin. While disappearance of luminal acid caused by aspirin or taurocholic acid was not altered by stress, the pepsin output in response to H+ increased significantly in the stressed rats. With exposure to various concentrations of HCl for 3 hr, disappearance of the luminal acid increased linearly with the grade of HCl under both conditions. Except for the concentration of 300 mM, the magnitude of the acid back-diffusion was triple in the normal condition, and the ratio of pepsin output/net flux of H+ was significantly increased by stress. Thus, (1) spontaneous acid back-diffusion decreased with stress, while diffusion induced by chemical barrier breakers remained the same; (2) the action of H+ diffused back into the mucosa did not always parallel the amount of diffusion determined from the loss of H+ in the lumen; (3) intramucosal H+ may be largely dissipated in normal mucosa; and (4) the initiation or aggravation of drug-induced mucosal damages by stress may be related to insufficiency of the H+ dissipating mechanisms.

Effects of 16,16-dimethyl-PGE2-methyl ester on aspirin- and indomethacin-induced gastric and intestinal lesions in mini pigs

Aspirin, 100 mg/kg, given only twice at intervals of 16 h to fasted mini pigs induced lesions in the body but had no effect on the antrum and small intestine. Indomethacin, 40 mg/kg, given once daily for 10 consecutive days to non-fasted mini pigs very weakly irritated the pig stomach but induced multiple superficial lesions in the jejunum and ileum. 16,16-Dimethyl-PGE2-methyl ester, 10 micrograms/kg in two divided doses or 20 micrograms/kg in four divided doses for 10 days, markedly inhibited the aspirin- or indomethacin-induced gastric and intestinal lesions in mini pigs, respectively.