Effects of Helicobacter pylori on gastritis, pentagastrin-stimulated gastric acid secretion, and meal-stimulated plasma gastrin release in the absence of peptic ulcer disease

OBJECTIVE

There is strong evidence accumulating that chronic infection with Helicobacter pylori (H. pylori) interferes with inhibitory pathways of the regulation of acid secretion. The increase in maximum acid output (MAO), and the increase in the sensitivity of the parietal cell to gastrin commonly observed in patients suffering from duodenal ulcer disease (DU), however, remains largely unexplained. Insufficient evidence is available concerning how these parameters are influenced by H. pylori infection in patients not suffering from peptic ulcer disease (PUD) and how they are related to H. pylori-induced gastritis. The aim of this study was to compare basal gastric acid secretion (BAO), MAO, and the sensitivity of the parietal cell to gastrin in H. pylori-positive and H. pylori-negative patients not suffering from PUD, and to study the relationship with their individual postprandial gastrin release and the degree of gastric antral and corpus gastritis.

METHODS

H. pylori status was assessed by CLO test and histology (two biopsies each from the antrum and the corpus) in 14 H. pylori-positive and 16 H. pylori-negative nonulcer patients of comparable age, weight and gender. Gastritis score was assessed by a pathologist, who was unaware of the acid secretory data. Following determination of BAO, the relation of pentagastrin and gastric acid secretion was established with a cumulative pentagastrin dose response curve for the dose range 0.03-6.0 microg/kg(-1) h(-1) and MAO (Vmax) and pentagastrin sensitivity (ED50) were determined. Basal and postprandial gastrin release was measured by radioimmunoassay.

RESULTS

There was a significant higher gastritis score in the H. pylori-positive compared with the H. pylori-negative subjects. The dose response curves of the pentagastrin stimulated gastric acid secretion were not different between H. pylori-positive and H. pylori-negative groups. No correlation was seen between the gastritis score, basal acid output (BAO) peak acid output (PAO), maximum acid output (MAO), ED50 values and the plasma gastrin values. There was, however, a considerable larger variation of the PAO and MAO data of the H. pylori-infected subjects and >50% of the respective data was above or below the relatively low range of the respective values of the noninfected subjects.

CONCLUSIONS

H. pylori-induced gastritis does not regularly enhance maximum acid output in nonulcer patients, nor does it modify the sensitivity of the parietal cell to gastrin. H. pylori infection is thus unlikely to be directly responsible for an increase of these parameters in DU disease. Our data support, however, the concept that chronic H. pylori infection can either enhance or attenuate maximum acid secretory capacity in certain subgroups of patients.

Comparison of acid inhibition by either oral high-dose ranitidine or omeprazole

BACKGROUND

High-dose once daily oral omeprazole dosing can inhibit acid secretion almost completely but several days elapse before maximum efficacy is established. The acid inhibitory effect obtained with high doses of a histamine H2-receptor antagonist is built up rapidly but has the tendency to fade--the term 'tolerance' has been applied to characterize this phenomenon.

METHODS

To obtain more information on the dynamics of acid inhibition during prolonged dosing, we compared the acid suppressory effects of oral high-dose omeprazole with high-dose ranitidine. Twenty-eight healthy volunteers were randomly assigned to a 2-week dosing with omeprazole or ranitidine in a double-blind, double-dummy, parallel-group study design. Omeprazole was given as 1 capsule of 40 mg mane and ranitidine as 2 tabs of 150 mg q.d.s. The median 24-h pH, daytime pH and night-time pH were measured by ambulatory continuous 24-h pH metry on days -8, -6, 1, 2, 7 and 14.

RESULTS

High reproducibility was observed for the two baseline acidity measurements. Ranitidine exerted its peak acid suppressant effect on day 1 of dosing; the degree of acid inhibition faded from day 2 to 7, with no significant change thereafter. The decline in antisecretory activity was more pronounced during the day than the night. In contrast, acid inhibition by omeprazole increased throughout the first week, and antisecretory activity was stable thereafter. Despite the considerable differences in median intragastric pH values at the end of the 14-day study, plasma gastrin levels were elevated to a similar degree with both medications.

CONCLUSIONS

This study confirms the 'tolerance' phenomenon previously observed with high-dose histamine H2-receptor antagonist dosing. The dynamics with which it occurs exclude a typical exaggerated first-dose response. Prolonged high-dose histamine H2-receptor dosing compromises the feedback mechanism regulating gastrin release, whilst this is maintained during dosing with omeprazole.

Pathophysiology and clinical relevance of Helicobacter pylori

Considerable knowledge has recently accumulated on the mechanism by which Helicobacter pylori (H. pylori) induces chronic gastritis. Although H. pylori is not an invasive bacterium, soluble surface constituents can provoke pepsinogen release from gastric chief cells or trigger local inflammation in the underlying tissue. Urease appears to be one of the prime chemoattractants for recruitment and activation of inflammatory cells. Release of cytokines, such as tumor necrosis factor alpha, interleukin 1 and 6, and oxygen radicals, leads to a further tissue inflammation accompanied by a potent systemic IgA and IgG type of immune response. Chronic inflammation and antigens on glandular epithelial cells lead to a progressive destruction with loss of the epithelial barrier function. Within the gastric mucosa, patches of intestinal metaplasia develop, which may be a risk factor for subsequent development of gastric carcinoma. Hyperacidity in duodenal ulcer patients induces gastric metaplasia in the duodenal bulb, which represents a target for H. pylori colonization and ulcer formation. H. pylori can be detected in the majority of patients with peptic ulcers and, compared to age-matched healthy people, it is also found more often in patients with dyspepsia and gastric carcinoma. Although H. pylori can be detected in healthy people, the marked reduction of the ulcer recurrence rate by eradication of H. pylori (80 percent versus 20 percent relapse within one year) suggests that H. pylori is a major risk factor for duodenal ulcer formation. The potential role of H. pylori in non-ulcer dyspepsia and carcinogenesis is under investigation. Current regimens aimed at eradicating H. pylori use a combination of several drugs that are potentially toxic. Since the risk of complications may exceed the potential benefit in most patients, eradication treatment should be limited to clinical trials and to patients with aggressive ulcer disease. New drug regimens, e.g., the combination of proton pump inhibitors with one antibiotic, may provide less toxic alternatives. Beyond ulcer treatment, effective and well-tolerated eradication regimens may have a place in prophylaxis of gastric carcinoma.