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

Reduced mucosal side-effects of acetylsalicylic acid after conjugation with tris-hydroxymethyl-aminomethane. Synthesis and biological evaluation of a new anti-inflammatory compound

Acetylsalicylic acid (ASA) causes adverse haemorrhagic reactions in the upper gastrointestinal (GI) tract, and previous results have suggested that combination therapy with 2-amino-2-(hydroxymethyl)-1,3-propanediol (Tris) could provide protection in this scenario. Based on this hypothesis, our aim was to develop a new compound from ASA and Tris precursors and to characterize the biological effects of ASA-Tris and the derivatives ASA-bis- and mono-hydroxymethyl-aminomethane (ASA-Bis, ASA-Mono, respectively) using in vivo and in vitro test systems. ASA or ASA conjugates (0.55mmol/kg, each) were administered intragastrically to Sprague-Dawley rats. Changes in the mucosal structure and in the serosal microcirculation were detected by in vivo imaging techniques, the plasma TNF-alpha, tissue xanthine oxidoreductase and myeloperoxidase activities, and liver cytochrome c changes were also determined. In two separate series, platelet aggregation and carrageenan arthritis-induced inflammatory pain were measured in control, ASA and ASA-Tris-treated groups. Severe mucosal injury and a significant decrease in serosal red blood cell velocity developed in the ASA-treated group and an ~2-fold elevation in proinflammatory mediator levels evolved. ASA-Tris did not cause bleeding, microcirculatory dysfunction, mucosal injury or an elevation in proinflammatory markers. The ASA-Mono and ASA-Bis conjugates did not cause macroscopic bleeding, but the inflammatory activation was apparent. ASA-Tris did not influence the cyclooxygenase-induced platelet aggregation significantly, but the inflammatory pain was reduced as effectively as in the case of equimolar ASA doses. ASA-Tris conjugation is an effective approach through which the GI side-effects of ASA are controlled by decreasing the cytokine-mediated progression of pro-inflammatory events.

Aspirin-like drugs cause gastrointestinal injuries by metallic cation chelation

Aspirin-like (nonsteroidal anti-inflammatory) drugs may cause injuries including ulcers to the gastrointestinal tract by chelation of the divalent and/or multivalent metallic cations in the gastrointestinal mucus and mucosa, as suggested by the chemical properties of these drugs and supported by experimental and clinical data.

Release of somatostatin, neurotensin and vasoactive intestinal peptide upon inhibition of gastric acid secretion by duodenal acid and hyperosmolal solutions in the conscious rat

The inhibitory effect of duodenal exposure to acid and hyperosmolal solutions on pentagastrin-stimulated gastric acid secretion was studied in conscious rats equipped with chronic gastric fistula and duodenal Thiry-Vella loop. The loop was challenged with saline, HCl or hyperosmolal polyethylene glycol. Gastric acid secretion was measured in samples from the gastric fistula. Gut peptide concentrations were measured in duodenal perfusates collected each 30 min, and in plasma samples collected both during stimulated acid secretion alone, and at the end of experiments in combination with luminal challenges of the loops. During pentagastrin-stimulated gastric acid secretion, luminal perfusion of the duodenal loop with acid caused inhibition of acid secretion (P < 0.001) and a prominent release of somatostatin both to the lumen (P < 0.001) and to the circulation (P < 0.05). Also, neurotensin (P < 0.01) and vasoactive intestinal peptide (P < 0.01) were released to the lumen, but not to the circulation. Upon perfusion of the duodenal loop with hyperosmolal polyethylene glycol, acid secretion was inhibited (P < 0.05) and somatostatin alone was released to the luminal side (P < 0.01). In conclusion, duodenal exposure to acid inhibits pentagastrin-stimulated gastric acid secretion and releases SOM to the circulation that may directly inhibit acid secretion. Concomitantly, somatostatin (SOM), neurotensin and vasoactive intestinal peptide are released to the lumen. Duodenal exposure to hyperosmolal polyethylene glycol inhibits acid secretion with a luminal release of SOM only. Thus, luminal acid and hyperosmolal solutions inhibit gastric acid secretion by separate mechanisms. After acid or hyperosmolal challenge, the release of SOM to the circulation indicates gastric acid inhibition in an endocrine manner, while a luminal release of gut peptides indicates a local peptide overflow that might be of importance via paracrine regulatory mechanisms in the intact animal.

Immunohistochemical localization of different forms of somatostatin in the gastrointestinal tract of the calf

The presence of two peptides that belong to the somatostatin family has been investigated in the calf gut. Somatostatin-14-like and Somatostatin-28-like peptides have been localized by a light microscopic immunohistochemical method. The method employed antibodies linked to colloidal gold particles that were revealed by a silver-enhancement step. Somatostatin-14-like peptide was only present in mucosal endocrine cells, which were detectable along the entire gut with the exceptions of the abomasal gastric proper glands and caecum. The cells were most abundant in cardiac and pyloric glands. Langerhans' islets also contained this type of endocrine cell. Somatostatin-28-like-immunoreactive endocrine cells were more abundant than the former cell type. They were present in the gastric proper glands and caecum where Somatostatin-14-like-immunoreactive cells were absent. They were as numerous as the former type of cell in the endocrine pancreas. The Somatostatin-28-like peptide was also detectable in the intramural nervous components of the abomasum and the intestine, in both perikarya and terminals. Our results show a possible heterogeneity of an endocrine cell type, which synthesizes and secretes somatostatin peptides. Our results also support the hypothesis that somatostatin-14 and somatostatin-28 peptides may have distinct functional roles, particularly in different species.

Alpha2-receptor-mediated inhibition of intraluminal release of gastric somatostatin in anaesthetized rats

The aim of the present study was to investigate how the sympathetic nervous system affects the vagally induced intragastric release of somatostatin and gastrin. Experiments were performed on anaesthetized rats in which the stomach was perfused with a dextrane solution (pH approximately 5.9) or dextrane buffer (pH 7.4). pH as well as gastrin and somatostatin levels were measured in the gastric perfusate when it had passed the stomach. Vagal stimulation caused a decrease in perfusate pH and an increase of the intraluminal output of gastrin and somatostatin when the stomach was perfused with the dextrane solution pH 5.9. Pretreatment with phentolamine (1 mg kg-1) significantly increased and pretreatment with clonidine (60 micrograms kg-1 h-1) significantly decreased somatostatin release caused by vagal stimulation, whereas gastrin levels remained largely unchanged. The effect of clonidine persisted in rats pretreated with indomethacin (5 mg kg-1), which per se potentiates the vagally induced luminal somatostatin release. When the stomach was perfused with the dextrane buffer pH 7.4, basal gastrin levels were significantly higher than during perfusion with the solution pH 5.9, whereas somatostatin levels remained unchanged. Neither somatostatin nor gastrin levels increased following vagal stimulation during gastric perfusion with the dextrane buffer pH 7.4. However, following pretreatment with phentolamine somatostatin levels increased during these conditions.

Relationship between gastric acid and elevated plasma somatostatinlike immunoreactivity after a mixed meal

The aim of this study was to examine whether hydrochloric acid plays a role mediating the post-prandial increase in plasma somatostatinlike immunoreactivity in normal subjects. Intravenous infusion of cimetidine was found to reduce by 45% the postprandial increment in plasma somatostatin-like immunoreactivity. This effect was reversed by concomitant intragastric administration of 0.1 N hydrochloric acid, which in previous studies in fasted subjects had not affected plasma somatostatinlike immunoreactivity. The effects of cimetidine on postprandial plasma gastrin were the inverse of those observed on postprandial somatostatin. There was a greatly enhanced increment in postprandial plasma gastrin during cimetidine infusion, which was reduced significantly toward control levels by concomitant intragastric infusion of hydrochloric acid. To exclude direct inhibition by cimetidine of nutrient-stimulated plasma somatostatinlike immunoreactivity we studied the effect of cimetidine on plasma somatostatinlike immunoreactivity stimulated by an intraduodenal infusion of fat. Cimetidine did not alter the incremental response of somatostatinlike immunoreactivity to intraduodenal fat infusion. These data show that cimetidine does not invariably reduce nutrient-stimulated plasma somatostatinlike immunoreactivity and are consistent with the hypothesis that the action of cimetidine in reducing the plasma somatostatin response to ingestion of a meal is a consequence of reduction of postprandial acid secretion. These data suggest that the postprandial elevation in plasma somatostatin observed in humans is mediated in part through postprandial secretion of gastric acid, which in turn acts to elevate plasma somatostatin.