Significance and regulation of gastric secretion of platelet-activating factor (PAF-acether) in man

Platelet-activating factor contracts guinea pig esophageal muscularis mucosae by stimulating extracellular Ca2+ influx through diltiazem-insensitive Ca2+ channels

Platelet-activating factor (PAF) is expected to increase esophageal motility. However, to the best of our knowledge, this has not been examined. Thus, we investigated the contractile effects of PAF on guinea pig (GP) esophageal muscularis mucosae (EMM) and the extracellular Ca2+ influx pathways responsible. PAF (10-9-10-6 M) contracted EMM in a concentration-dependent manner. PAF (10-6 M)-induced contractions were almost completely suppressed by apafant (a PAF receptor antagonist, 3 × 10-5 M). In EMM strips, PAF receptor and PAF-synthesizing/degrading enzyme mRNAs were detected. PAF (10-6 M)-induced contractions were abolished by extracellular Ca2+ removal but were not affected by diltiazem [a voltage-dependent Ca2+ channel (VDCC) inhibitor, 10-5 M]. PAF (10-6 M)-induced contractions in the presence of diltiazem were significantly suppressed by LOE-908 [a receptor-operated Ca2+ channel (ROCC) inhibitor, 3 × 10-5 M], SKF-96365 [an ROCC and store-operated Ca2+ channel (SOCC) inhibitor, 3 × 10-5 M], and LOE-908 plus SKF-96365. Among the tested ROCC/SOCC-related mRNAs, Trpc3, Trpc6, and Trpv4/Orai1, Orai3, and Stim2 were abundantly expressed in EMM strips. These results indicate that PAF potently induces GP EMM contractions that are dependent on extracellular Ca2+ influx through ROCCs/SOCCs, and VDCCs are unlikely to be involved.

Putative effect of Helicobacter pylori and gastritis on gastric acid secretion in cat

Helicobacter pylori may increase or inhibit gastric acid. We studied acid variations and plasma gastrin in cats harboring Helicobacter felis, harboring H. pylori, or free of gastric pathogens with reference to thioperamide (H(3) receptor antagonist) and SR-27417A (PAF receptor antagonist). In cats harboring H. felis, gastric mucosa were histologically normal. After H. felis eradication, pentagastrin-stimulated acid secretion was increased (40%) compared with the situation before eradication. Thioperamide abolished this inhibitory effect of H. felis, whereas SR-27417A did not. Basal and meal-stimulated plasma gastrin levels were not affected by eradication therapy. Acid secretion was inhibited (-80%) in week 3, increased from weeks 5 to 9, and remained constant for up to 42 weeks after H. pylori infection. SR-27417A had no effect on acid secretion before week 8 but inhibited it thereafter, and thioperamide increased it (20%) only before week 7 in those cats. Helicobacter inhibits gastric acid via an H(3) receptor pathway. Inflammatory mediators are thus involved in adaptation to the inhibitory effects of H. pylori on acid secretion.

Mechanosensitive properties of gastric vagal afferent fibers in the rat

Single, teased fiber recordings were made from the decentralized right cervical vagus nerve (hyponodal) of the rat. A total of 67 afferent fibers that responded to gastric distension (GD) were studied: 9 fibers were stimulated by phasic balloon GD, 58 by more natural fluid GD. All balloon GD-responsive fibers had resting activity (3.1 imp/s), and 57/58 fluid GD responsive fibers had resting activity (1.3 imp/s). All balloon GD-responsive fibers exhibited a dynamic response to phasic distension followed by slow adaptation, whereas fluid GD-responsive fibers exhibited increasing responses as intragastric pressure increased, followed typically by slow adaptation. Responses to graded GD were studied in all fibers, and all gave increasing responses to increasing pressures (5-60 mmHg). Thresholds for response varied between 0 and 18 mmHg. Mean response thresholds for two durations of fluid GD (30 and 60 s) were 5.6 and 3.9 mmHg; the mean response threshold to phasic balloon GD (30 s duration) was 5.3 mmHg. The potential sensitizing effect of platelet activating factor (PAF, 50 or 100 ng. kg(-1). min(-1) for 20 min) infused into the gastric artery was studied in 20 fibers. Fifteen fibers exhibited an increase in spontaneous activity; intragastric pressure also slightly increased during PAF infusion. The increase in activity produced by PAF was attenuated in the presence of the PAF receptor antagonist WEB 2086. After PAF-induced acute inflammation of the stomach, three of five fibers studied did not exhibit any change in response to graded GD. The present study characterized distension-sensitive afferent fibers in the right cervical vagus innervating the stomach of the rat by balloon GD and fluid GD. The results document that all distension-sensitive gastric vagal afferent fibers encoded the intensity of GD, but none had response thresholds in what might be considered the noxious range. PAF infusion activated mechanosensitive gastric vagal afferent fibers, but acute inflammation produced by PAF did not sensitize responses to GD.

Helicobacter pylori

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Helicobacter pylori

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Enhanced levels of chemiluminescence and platelet activating factor in urease-positive gastric ulcers

Helicobacter pylori are believed to play an important role in the formation of gastric ulcer in a syndrome characterized by a high urease activity. On the other hand, the production of oxygen radicals and platelet activating factor (PAF) is enhanced in gastric ulcers. The present study is designed to investigate the relationship between the different aspects of gastric mucosal injury, urease activity, oxygen radical production, and PAF content in gastric specimens. Biopsy specimens taken from 35 gastric ulcer patients were studied. Urease activity was detected by a rapid urease test (CLO). Oxygen radical production was measured as a value of luminol-dependent chemiluminescence (ChL) and PAF content was determined by radioimmunoassay in the biopsy samples. The CLO-positive rate was significantly higher in the gastric ulcer group in comparison with that in controls. ChL values and PAF content were significantly increased in gastric ulcers, especially in CLO-positive specimens. The CLO-positive rate, ChL values, and PAF content were also found to be increased at a distant site beyond the ulcer lesions. During the course of macroscopic ulcer healing of CLO-positive cases, the CLO positive level and the ChL values were not significantly decreased, although PAF content was significantly lower. Enhanced oxygen radical and PAF production were observed not only in the ulcer region but also at a distant site from the ulcer in the urease-positive gastric mucosa. The persistent enhancement of ChL values during the healing stage of urease-positive gastric ulcers suggests its involvement in the recurrence of gastric ulcers.

Gastric secretion of platelet activating factor and precursors in healthy humans: effect of pentagastrin

The release of platelet activating factor (PAF-ACETHER or PAF) and its precursors in the gastric lumen was assessed in 13 normal subjects in basal condition and after stimulation by gastrin. Acid, pepsin, and sialic acid outputs were determined under the same conditions. Gastric juice was collected using a nasogastric tube after overnight fast in basal condition for 60 minutes, then under pentagastrin infusion (6 micrograms/kg/hr for 60 minutes). Platelet activating factor was detected at low concentration in 4/13 subjects under basal condition (mean (SEM) 1.2 (0.6) pg/hr) while high concentrations of lyso platelet activating factor (6.1 (1.8) microgram/hr) and of alkyl-acyl-glycerophosphocholine (AAGPC) (11.5 (3) micrograms/hr) were found in 13 and 11 subjects, respectively. Platelet activating factor was not detected during pentagastrin infusion, while lyso platelet activating factor and alkyl-acyl-glycerophosphocholine were detected in 13 and in 12 subjects, respectively. Compared with the basal condition these platelet activating factor precursors increased significantly (p < 0.001) going up to fivefold baseline (31.8 (6.8) micrograms/hr and 53 (9.3) micrograms/hr respectively) in response to pentagastrin. There was a positive correlation between platelet activating factor precursors and acid or pepsin output but not between platelet activating factor precursors and sialic acid. As sialic acid may be considered an index of mucus glycoprotein degradation, it seems that gastrin stimulation of gastric epithelial cells results in a concomittant secretion of platelet activating factor precursors, acid, and pepsin irrespective of mucus glycoprotein degradation.