Gastrocytoprotection by colloidal bismuth subcitrate (De-Nol) and sucralfate. Role of endogenous prostaglandins.

This study compares the gastroprotective effects of colloidal bismuth subcitrate (De-Nol) with those of sucralfate and a methylated analogue of prostaglandin E2 (PGE2) against acute gastric lesions induced by acidified aspirin and absolute ethanol in rats. Both De-Nol and sucralfate given orally prevented dose dependently the formation of gastric lesions by these ulcerogens, De-Nol being, respectively, twice and seven times more potent, on a weight basis, than sucralfate. As the gastroprotective activities of both De-Nol and sucralfate on ethanol lesions can be reversed by pretreatment with indomethacin and as De-Nol and sucralfate increase the mucosal generation and luminal release of PGE2, we postulate that mucosal prostaglandins may be involved in the mechanism of action of these drugs on the gastric mucosa.

Gastric mucosal protection by agents altering gastric mucosal sulfhydryls. Role of endogenous prostaglandins.

Intragastric administration of sulfhydryl-containing cysteamine or sulfhydryl-oxidizing diethylmaleate caused a dose-dependent reduction in the mean area of gastric lesions induced by absolute ethanol. The protective effects of these agents are abolished by the sulfhydryl blocker N-ethylmaleimide, while indomethacin, a potent inhibitor of cyclooxygenase, caused only about 50% reduction in this protection. This study indicates that mucosal generation of prostaglandins contributes to the gastric cytoprotection by these agents administered intragastrically, but endogenous sulfhydryls are also involved in the gastric mucosal protection by sulfhydryl-containing or sulfhydryl-oxidizing compounds.

Studies on the gastroprotective and ulcer-healing effects of colloidal bismuth subcitrate.

We investigated the gastroprotective effects of colloidal bismuth subcitrate (CBS, De-Nol) in comparison with agents such as sucralfate and methylated PGE2. Both CBS and sucralfate given orally prevented dose dependently the formation of gastric lesions by acidified aspirin, ethanol and restraint stress, CBS being more potent on a weight-to-weight basis than sucralfate. CBS and sucralfate were also equally effective in enhancing the healing rate of chronic gastric and duodenal ulcer induced by serosal application of acetic acid, while methylated PGE2 was completely ineffective in this model. Non-colloidal bismuth subnitrate, in contrast to CBS, was ineffective against stress-induced lesions. CBS stimulated mucosal generation and luminal release of PGE2 dose dependently.

Antiulcer and gastroprotective effects of solon, a synthetic flavonoid derivative of sophoradin. Role of endogenous prostaglandins.

Solon is a synthetic isoprenyl flavonoid derived from sophoradin which is isolated from the root of an ancient Chinese plant. Solon was administered orally or intraperitoneally to rats. It inhibited dose dependently gastric ulcers produced by acidified aspirin, water immersion and restraint stress. Solon was also gastroprotective for the stomach as it reduced dose dependently the gastric necrotic lesions induced by absolute ethanol given orally. The degree of gastroprotection decreased with time, the optimal effects occurring 60-90 min after oral administration. Pretreatment with indomethacin partly prevented the gastroprotective effects of Solon. When given alone to fasted rats, Solon increased dose dependently the mucosal content of prostaglandins (PG), suggesting that the protective effects of this drug may be mediated at least in part by endogenous PG.

Advances in the understanding of the mechanism of cytoprotective action by colloidal bismuth subcitrate.

This study was designed to compare the gastroprotective effects of colloidal bismuth subcitrate (CBS) with those of sucralfate and methylated analog of prostaglandin E2 (PGE2) against acute gastric lesions induced by absolute ethanol, acidified aspirin (ASA), and water immersion and restraint stress in rats. When given orally, both CBS and sucralfate prevented in a dose-dependent way the formation of gastric lesions induced by all three ulcerogens, CBS being about 7, 2, and 20 times more potent, respectively on a weight-to-weight basis than sucralfate. Methylated PGE2 was also highly effective against these ulcerogens. Bismuth subnitrate was ineffective against acute gastric lesions induced by stress conditions. The protection of both CBS and sucralfate was reversible when the animals were pretreated with indomethacin to suppress the generation of endogenous prostaglandins. Since CBS and sucralfate increased the production of PGE2 in the gastric mucosa, we postulate that their gastric protective action may be mediated, at least partly, by mucosal prostaglandins.

Role of prostaglandin and thromboxane biosynthesis in gastric necrosis produced by taurocholate and ethanol.

The effects of a new selective inhibitor of thromboxane biosynthesis, OKY-1581, and a potent inhibitor of cyclooxygenase, indomethacin, on gastric mucosal lesions induced by taurocholate or ethanol and mucosal generation of prostaglandins have been studied in rats. OKY-1581 prevented, dose dependently, the formation of taurocholate- but not ethanol-induced gastric necrosis, and this effect was accompanied by an increase in gastric mucosal generation of prostaglandin E2 and I2-like activity and a reduction in the thromboxane generation during platelet aggregation. OKY-1581 enhanced the cytoprotective action of "mild" irritants such as 5 mM taurocholate against gastric damage by 100 mM taurocholate, whereas indomethacin produced opposite effects. This study indicates: (1) the inhibition of thromboxane biosynthesis results in increased generation of prostaglandins which seems to contribute to the gastric mucosal integrity and, (2) thromboxanes may be involved in the pathogenesis of taurocholate-induced gastric mucosal lesions.

Gastric cytoprotection by agents altering gastric mucosal sulfhydryl compounds: role of endogenous prostaglandins.

Intragastric administration of cysteamine or diethyl maleate caused a dose-dependent reduction in the mean area of gastric lesions induced by absolute ethanol but failed to affect gastric ulcerations produced by acidified aspirin. Mucosal levels of glutathione were increased with cysteamine and reduced with diethyl maleate and did not correlate with the protective action of these agents on ethanol-induced mucosal lesions. The protective effects of these agents probably involved mucosal generation of prostaglandins, because pretreatment with indomethacin or aspirin, potent inhibitors of cyclooxygenase, partially prevented this protection. This study indicates that the mucosal generation of prostaglandins contributed, at least in part, to the gastric cytoprotection by agents altering mucosal contents of sulfhydryl compounds.

Gastric cytoprotection by acetazolamide: role of endogenous prostaglandins.

This study was designed to determine the influence of acetazolamide, a potent inhibitor of carbonic anhydrase, on the formation of gastric mucosal lesions induced by acidified aspirin (ASA) or absolute ethanol and on gastric cytoprotection induced by prostaglandin E2 (PGE2). Acetazolamide prevented dose-dependently ethanol-induced gastric lesions and this effect was accompanied by an increased biosynthesis of mucosal PGs, indicating that endogenous PGs may be involved in cytoprotection by acetazolamide. This is supported by the finding that acetazolamide failed to affect gastric ulcerations produced by acidified ASA when mucosal PG biosynthesis was almost completely suppressed. Pretreatment with acetazolamide did not influence the protective action of PGE2 on ethanol-induced mucosal lesions and only slightly inhibited the protective effect of PGE2 on ASA-induced gastric ulcerations. This study indicates that: (1) acetazolamide prevents ethanol- but not ASA-induced gastric mucosal lesions probably via stimulation of PG biosynthesis and (2) gastric alkaline secretion, mediated by carbonic anhydrase, is probably not an essential mechanism responsible for this cytoprotection induced by PGE2.

Role of locally generated prostaglandins in adaptive gastric cytoprotection.

This study was designed to determine the role of mucosal generation of prostaglandins (PGs) in the ability of mild irritants (20% ethanol or 5% NaCl) to protect against the formation of mucosal lesions caused by necrotizing agents (100% ethanol or 25% NaCl) or acidified aspirin (ASA). Mild irritants protected damage from necrotizing agents but not from ASA. This protection was accompanied by increased mucosal generation of PGE2 and PGI2-like substances. Exogenous PGE2 and PGI2 applied topically to the gastric mucosa in a nonantisecretory dose greatly inhibited the formation of lesions induced by either necrotizing agents or ASA. Pretreatment with indomethacin, which suppressed the generation of mucosal PGs augmented formation of lesions by necrotizing agents and partly counteracted the protective effect of mild irritants. We conclude that mild irritants, and exogenous PGs inhibit the formation of gastric lesions by necrotizing agents, at least in part, by mucosal generation of PGs.

Prevention of ethanol and aspirin-induced gastric mucosal lesions by paracetamol and salicylate in rats: role of endogenous prostaglandins.

Paracetamol or sodium salicylate given intragastrically 30 minutes before the administration of absolute ethanol or acidified aspirin dose-dependently reduced the formation of mucosal lesions. The generation of gastric mucosal prostaglandin-like activity increased with ethanol and was completely suppressed by acidified aspirin. Paracetamol or sodium salicylate given alone increased the generation of mucosal prostaglandin-like material. Indomethacin, the prostaglandin synthesis inhibitor, suppressed this effect and inhibited the protective influence of paracetamol or sodium salicylate on the production of gastric lesions.

Gastric cytoprotection by pirenzepine. Role of endogenous prostaglandins.

This study compared the effects of pirenzepine, a novel selective antimuscarinic agent, and PGE2 applied topically on the gastric mucosa or parenterally on gastric secretion and formation of ASA and ethanol-induced gastric ulcerations in rats. Pirenzepine given topically in nonantisecretory dose prevented the formation of gastric ulcerations induced by ASA + 0.15 M HCl and absolute ethanol. These cytoprotective effects were comparable to those observed after PGE2 administered intragastrically or subcutaneously. Pirenzepine did not affect ulcer formation by ASA combined with 0.30 M HCl, whereas PGE2 was fully effective under these conditions. The cytoprotective action of pirenzepine was not accompanied by any change in the mucosal generation of PGs, indicating that endogenous PGs do not contribute to the cytoprotective property of this agent.

Aspirin-induced gastric ulcers in cats. Prevention by prostacyclin.

Gastric ulcers were produced in conscious cats in 3 hr by simultaneous intravenous or intragastric administration of acetylsalicylic acid (ASA), plus intravenous infusion of histamine (80 micrograms/kg/hr), pentagastrin (8 micrograms/kg/hr), or intragastric instillation of HCl. The formation of these ulcers was accompanied by almost complete inhibition of prostaglandin (PG) biosynthesis, suggesting that the withdrawal of normal protection of gastric mucosa by PGs may be major factor in pathogenesis of ASA-induced gastric lesions. Prostacyclin (PGI2), infused at a dose producing about 50% inhibition of histamine or pentagastrin-induced acid secretion, significantly reduced the formation of gastric ulcers produced by ASA + histamine or pentagastrin. Inhibition of gastric acid secretion by about 50% using ranitidine, a new H2-receptor antagonist, also decreased the formation of gastric ulcers induced by ASA + gastric secretagogue, but the degree of this reduction was significantly smaller than after PGI2. In addition, PGI2 decreased significantly the severity of gastric ulcers produced by a combination of ASA plus gastric perfusion of HCl, the antiulcer effect being more pronounced when PGI2 infusion was started prior to, rather than during, ASA administration. This study confirms that the administration of ASA plus gastric secretagogue or gastric instillation of HCl is a reliable model of gastric ulcerations probably resulting from withdrawal of biosynthesis of mucosal PGs and shows that PGI2 is capable of preventing the formation of these ulcers by means other than its effect on gastric acid secretion.

Role of mucosal prostaglandins and DNA synthesis in gastric cytoprotection by luminal epidermal growth factor.

This study compares the effect of epidermal growth factor and prostaglandins (PGE2 or PGI2), applied topically to gastric mucosa, on gastric secretion and formation of ASA-induced gastric ulcerations in rats. Epidermal growth factor given topically in non-antisecretory doses prevented dose-dependently the formation of ASA-induced ulcers without affecting prostaglandin generation but with a significant rise in DNA synthesis in the oxyntic mucosa. The anti-ulcer effect of topical prostaglandins was also accompanied by an increase in DNA synthesis. This study indicates that topical epidermal growth factor, like PGE2 or PGI2, is cytoprotective and that this cytoprotection is not mediated by the inhibition of gastric secretion or prostaglandin formation but related to the increase in DNA synthesis in oxyntic mucosa.

Gastric cytoprotection by prostaglandins, ranitidine, and probanthine in rats. Role of endogenous prostaglandins.

Intragastric administration of aspirin (ASA) plus 0.15 M HCl to fasted rats produced typical gastric ulcers accompanied by almost complete disappearance of mucosal prostaglandins (PGs). Pretreatment with various exogenous PGs that were biologically inactive (e.g. 6-keto-PGF1 alpha or PGF2 beta) or active (PGE2 and PGI2) but used in non-antisecretory doses prevented the formation of these gastric lesions ('cytoprotection'). Besides PGs, antisecretory compounds such as ranitidine, a new H2-receptor antagonist, and probanthine were also found to be cytoprotective, even when given in non-antisecretory doses. Mucosal generation of PGs in animals treated with ASA and HCl plus ranitidine or probanthine was very low and not significantly different from those receiving only ASA and HCl. Thus, the cytoprotection appears to be the property not only of PGs but also of conventional gastric antisecretory compounds such as H2-receptor antagonists or anticholinergics. This cytoprotection can be demonstrated under conditions excluding any role of gastric secretory inhibition and in the absence of endogenous PGs.

Prostaglandin E2 in gastric mucosa and its role in the prevention of ulcers induced by acetyl salicylic acid in cats.

Gastric mucosa of the cat generates PGE2 activity at a significantly higher concentration in the antral 59.25 +/- 7.42 ng/g) than in the oxyntic (28.06 +/- 4.50 ng/ml) gland area. Intravenous (i.v.) infusion of histamine 80 micrograms/kg/h) or intragastric (i.g.) instillation of 0.1 N HCl (4 mEq/h) for 3 h significantly decreased the generation of PGE2 in antral and fundic mucosa, but did not result in the formation of gastric lesions. Aspirin (ASA) given i.v. or i.g. for 3 h caused a further fall in the generation of PGE2 in the mucosa and when combined with i.v. histamine or i.g. HCl, it caused almost complete disappearance of PGE2 activity and the formation of antral ulcers in all tested cats. Exogenous PGE2, given i.v. in a dose (30 micrograms/kg/h) reducing histamine-stimulated (80 micrograms/kg/h) acid secretion by about 50%, prevented almost completely the formation of gastric ulcers induced by a combination of ASA plus i.v. histamine or i.g. HCl. This study indicates that the gastric mucosa generates PGE2 which is capable of preventing gastric ulcers induced by ASA combined with histamine or mucosal acidification.

Role of prostaglandins in the formation of aspirin-induced gastric ulcers.

Gastric mucosa of the rat generates both PGE2 and PGI2 activity in significantly higher concentrations in the antrum than in the fundus. Aspirin, given intravenously or intragastrically in doses producing gastric mucosal lesions, causes a dose-dependent decrease in the generation of mucosal PGE2 and PGI2, which is further enhanced by gastric perfusion of HCl. Exogenous PGE2 and PGI2 administered intravenously in doses not affecting gastric secretion almost completely prevented the formation of aspirin-induced ulcers. This study indicates that gastric mucosa is capable of generating PGE2 and PGI2 which may be responsible for its protection against chemical injury.