Gastric prostaglandin E2 release induced by aluminium hydroxide and aluminium hydroxide-containing antacids in rats. Effect of low doses and citric acid

Stimulation of prostaglandin biosynthesis mediates gastroprotective effect of rebamipide in rats

The concept that gastroprotection by agents such as mild irritants, antacids, or sucralfate is prostaglandin (PG)-mediated has been challenged recently. These agents do not reproducibly stimulate prostaglandin formation, and indomethacin does not effectively attenuate their protective potency. Rebamipide is a novel antiulcer compound. This study was designed to clarify whether eicosanoids contribute to the gastroprotective activity of the drug. In the rat stomach, rebamipide (100 and 500 mg/kg, intraperitoneally) slightly increased release of PGE2, 6-keto-PGF1 alpha, thromboxane B2, and the metabolite 15-keto-13,14-dihydro-PGE2 from mucosal fragments incubated ex vivo and significantly enhanced secretion of these products into the lumen, resulting in gastric juice eicosanoid levels exceeding those in controls several-fold. Mucosal formation of leukotriene (LT) C4 was not affected by rebamipide. Rebamipide caused substantial protection against gastric damage produced by ethanol, which was antagonized by pretreatment with indomethacin (0.1-5 mg/kg, subcutaneously). The dose-response relationship of indomethacin for inhibition of prostaglandin formation and rebamipide-induced protection correlated well and 5 mg/kg indomethacin completely prevented the protective effect of rebamipide. The results indicate that: (1) in contrast to most other protective agents, protection by rebamipide involves the endogenous prostaglandin system; (2) the increase in prostaglandin formation results from stimulation of biosynthesis, and not inhibition of degradation; (3) gastroprotection by rebamipide occurs despite increased thromboxane formation and is not associated with reduced generation of LTC4; and (4) determinations of gastric juice eicosanoids seem to be particularly useful to evaluate effects of agents increasing formation of cyclooxygenase products in the stomach.

Role of eicosanoids, nitric oxide, and afferent neurons in antacid induced protection in the rat stomach

The mechanism underlying the mucosal protective effect of antacids is still unclear. This study shows that in rats the aluminum containing antacid, hydrotalcit, induces dose dependent protection against gastric mucosal damage caused by ethanol or indomethacin which is considerably enhanced by acidification. Hydrotalcit did not increase gastric mucosal formation or the intraluminal release of prostaglandins, and did not prevent the increase in mucosal leukotriene C4 formation in response to ethanol. Pretreatment with indomethacin did not attenuate the protective effect of unmodified or acidified hydrotalcit. Furthermore, hydrotalcit significantly reduced the gastric damage caused by indomethacin even when it was administered up to 2 hours after the ulcerogen. In indomethacin treated rats, simultaneous administration of hydrotalcit did not affect the concentrations of indomethacin in serum or inflammatory exudates nor did it attenuate the inhibition of prostaglandin release into the exudates. In hydrotalcit treated rats there was no attenuation of the increase in sulphidopeptide leukotriene release or decrease in leukocyte influx into inflammatory exudates elicited by indomethacin administration. Functional ablation of afferent neurons and inhibition of endogenous nitric oxide partially antagonised the protective effect of unmodified, but not of acidified, hydrotalcit. It is concluded that (i) the protective effect of unmodified and acidified hydrotalcit is independent of the eicosanoid system; (ii) protection against indomethacin induced gastric lesions does not require treatment before dosing of the ulcerogen and does not interfere with absorption and anti-inflammatory actions of indomethacin; (iii) endogenous nitric oxide and afferent neurons contribute partly to the effect of unmodified, but not of acidified, hydrotalcit suggesting that different mechanisms mediate their mucosal protective activity.

Comparison of low-dose antacids, cimetidine, and placebo on 24-hour intragastric acidity in healthy volunteers

Low-dose aluminium (Al) antacids are effective in promoting ulcer healing and symptomatic relief in peptic ulcer patients, although the effect on intragastric acidity is very weak. In this randomized, double-blind study, 24-hr intragastric acidity was compared in 11 healthy volunteers, treated with a low-dose Al antacid regimen (1 tablet four times a day), cimetidine (800 mg at bedtime) and placebo, using the double-dummy technique. Standardized meals were given at 8 AM, noon, and 5 PM. Medication was given 1 hr after meals and at bedtime. Intragastric acidity was recorded with a nasogastric monocrystant antimony pH catheter, connected to an ambulatory digital data recorder. No significant difference in intragastric acidity was observed between antacid and placebo treatment. Treatment with cimetidine reduced circadian and nocturnal (but not diurnal) intragastric acidity significantly, as compared to both placebo and antacid treatment. The results support the hypothesis that Al antacids promote peptic ulcer healing by other mechanisms than acid neutralization.

Acute effects of antacids on gastric juice components in duodenal ulcer patients

In 10 duodenal ulcer patients gastric juice was aspirated every 10 min for 20 min before and 200 min after sham feeding. One antacid tablet or placebo was given 80 min after the sham feeding. Analyses of the aspirates showed that antacids reduced mean hydrogen ion activity and pepsin concentration significantly for 40 and 60 min, respectively, and increased phospholipid concentration for 30 min, compared with placebo. Highest mean pH was 2.52. The percentage of pH readings at or above pH levels of 2, 3, and 4 during the 2 h period following antacid administration was 29, 10, and 2%, respectively. No significant differences between antacid and placebo were found regarding intragastric concentrations of bile acids and prostaglandin E2. When one antacid tablet was administered 80 min after a real meal, the effect on intragastric pH was similarly weak, but lasted slightly longer. Acid neutralization' alone can hardly explain the ulcer-healing effect of low-dose antacids. Antacid-induced increase in intragastric concentration of phospholipids is a new and potentially important observation.

Antacids in gastric ulcer treatment: evidence of cytoprotection

Antacids are more effective than placebo, and their efficacy is comparable to that of H2-blockers in gastric ulcer healing even though the healing time is about 2 weeks longer than with H2-blockers. Some observations in animals and healthy subjects may indicate that antacids (particularly those containing aluminium hydroxide) have a protective effect on the gastroduodenal mucosa in that they increase the production of prostanoids and sulphydryl-containing compounds. We showed that 10 days' treatment with high-dose antacids (Maalox TC) is able to increase 6-keto-PGF1 alpha production from cultured biopsy specimens of patients with gastric ulcer. These data could constitute a further indication in the treatment of peptic disease.

Acute damage of gastroduodenal mucosa by acetylsalicylic acid: no prolonged protection by antacids

Twenty healthy volunteers participated in a double-blind, crossover study to evaluate endoscopically whether low-dose antacids have any prolonged and pH-independent protective capacity against gastroduodenal mucosal damage induced by acetylsalicylic acid. Antacid or placebo one tablet q.d.s. was given for 1.5 days. Acetylsalicylic acid (1.5 g) was administered 3 h after the last dose of antacid/placebo, and gastroscopy was performed 1 h thereafter. Thirteen of 20 subjects showed a decrease in total damage with antacids as compared with placebo, but the difference did not reach statistical significance. Thus, protection by antacids against acetylsalicylic acid-induced gastric mucosal lesions could not be documented at a time when intragastric pH presumably had returned to normal.

Antacids reduce Campylobacter pylori colonization without healing the gastritis in patients with nonulcer dyspepsia and erosive prepyloric changes

Antral biopsy specimens from 89 consecutive patients with nonulcer dyspepsia and erosive prepyloric changes included in a prospective, randomized, double-blind 4-wk study of the effect of an aluminum-magnesium antacid (120 mmol/day) or pirenzepine (50 mg b.i.d.) vs. placebo were examined histologically. Campylobacter pylori (CP) was found by light microscopy of silver-stained sections in 25 patients (28%). Campylobacter pylori-positive patients were on average older than CP-negative patients (p = 0.02). There was a strong association between CP colonization and acute inflammation (p less than 0.001), both being rare in the absence of chronic inflammation. During treatment with antacids, the density of CP decreased (p less than 0.001) without any improvement of the inflammatory reaction. On the contrary, the number of patients with gastritis tended to increase after antacids as compared with placebo (p less than 0.10). A separate analysis showed no symptomatic effect of the drugs. Thus, neither nonulcer dyspepsia nor erosive prepyloric changes are strongly associated with antral CP colonization or acute inflammation. Aluminum-magnesium antacids may suppress antral CP infection without healing the gastritis or relieving symptoms.