Do prostaglandins mediate the somatostatin preventive effect on gastric lesion?

Role of acute elevation of portal venous pressure by exogenous glucagon on gastric mucosal injury in rats with portal hypertension

Time-course studies revealed the increased susceptibility of the gastric mucosa to noxious injury in portal hypertension correlates with the level of elevated portal venous pressure and hyperglucagonemia. Whether acute elevation of portal venous pressure by exogenous glucagon aggravates such injury is not known. We tested the hypothesis that glucagon in a dose sufficient to acutely elevate portal venous pressure aggravates noxious injury of the gastric mucosa in rats with portal hypertension. Infusion of a portal hypotensive dose of somatostatin should reverse these changes. In anesthetized rats with portal vein ligation, glucagon, somatostatin or the combination was administered intravenously in a randomized, coded fashion. Acidified ethanol-induced gastric mucosal injury was determined. Portal venous pressure and gastric mucosal perfusion and oxygenation (reflectance spectrophotometry) were monitored to confirm the effects of the respective intravenous treatments. Exogenous glucagon exacerbated acidified ethanol-induced gastric mucosal injury. The exacerbation was attenuated by somatostatin. These changes paralleled the portal hypertensive and hypotensive effects of glucagon and somatostatin, respectively. Our data suggest that a unique mechanism is triggered with the onset of portal hypertension. In an antagonistic manner, glucagon and somatostatin modulate this novel mechanism that controls portal venous pressure and susceptibility of the gastric mucosa to noxious injury.

Newer agents available for treatment of stress-related upper gastrointestinal tract mucosal damage

Results of animal studies and human clinical trials assessing the efficacy of newer agents in the treatment of stress-related mucosal damage have been reviewed. Currently available data suggest that prostaglandin treatment is as effective in preventing and treating stress-induced mucosal injury as more established therapeutic modalities, but that the proposed efficacy of somatostatin infusion and tranexamic acid administration is highly suspect. Promising agents yet to be evaluated include omeprazole, allopurinol, and epidermal growth factor.

Stress-related mucosal damage: critical evaluation of potential new therapeutic agents

Cell injury produced by hydrochloric acid is the final common denominator for stress-related mucosal damage. Actions of therapeutic agents designed to prevent such damage are directed toward either inhibiting acid secretion or stimulating protective mechanisms. Newer agents that fall into the former category include omeprazole, an inhibitor of the H+-K+-ATPase pump, prostaglandins, and somatostatin. In addition to inhibiting acid, prostaglandins stimulate mucus and bicarbonate secretion and therefore provide a two-pronged protective action. Tranexamic acid is an antifibrinolytic agent that is postulated to promote clotting at bleeding sites in upper gastrointestinal lesions. Analyses of composite data suggest that (1) prostaglandin E preparations appear to be as effective as currently recognized forms of therapy, such as antacid and H2-receptor antagonist administration; (2) little enthusiasm can currently be generated for use of somatostatin or tranexamic acid; and (3) omeprazole is a theoretically attractive agent that remains to be tested in the prophylactic treatment of gastrointestinal ulceration due to severe stress.

Effect of intragastric pH, prostaglandins and prostaglandin synthesis inhibitors on the release of gastrin and somatostatin into the gastric lumen of anaesthetized rats

The object of the present work was to study the influence of antral pH, of aspirin and indomethacin, and of prostaglandins A2, E1 and E2 on the intragastric output of somatostatin and gastrin induced by electrical vagal stimulation (5 V, 2 ms, 2, 5 and 10 Hz). Experiments were performed on anaesthetized rats in which the stomach was perfused with a dextran solution (pH approximately 1.5 to approximately 6). To assess the effect of vagal stimulations on gastric acid secretion and on gastrin and somatostatin release, pH as well as somatostatin and gastrin levels was recorded in the perfusate effluent. During perfusion of the stomach with dextran solution, pH approximately 6, vagal stimulation at 10 Hz decreased perfusate pH to 1.3 and gastrin and somatostatin were released at a ratio of 2:1. Less gastrin and more somatostatin (ratio 0.1:1) was released by the same stimulation when the stomach was pre-perfused with acid solution (pH approximately 1.5), although also in these experiments the pH of the perfusate fell to 1.3. When vagal stimulations were performed after the rats had been pretreated with aspirin or indomethacin, more somatostatin than gastrin was detected in the perfusate independently of the perfusate pH. The vagally induced intraluminal release of somatostatin occurring in aspirin-treated animals was abolished by a low dose of atropine (0.05 mg kg-1) or by a simultaneous infusion of prostaglandin E1 (30 micrograms kg-1 h-1).