[Influence of gastric juice pH on the metabolism of vitamin C in gastric mucosa and juice].

UNLABELLED

Vitamin C is present as ascorbic acid (Asc) with antioxidative properties and as its oxidation product dehydroascorbic acid (dAsc). Asc is actively transported from blood to gastric juice where it prevents formation of carcinogenic nitrosamines and protects mucosa from reactive oxygen species. Another important function of gastric mucosa is proton pump-dependent secretion of hydrochloric acid. The pump maintains high pH gradient between gastric juice and plasma. The aim of the work was to analyse relations between gastric juice pH and concentrations of Asc and dAsc in plasma, gastric mucosa and juice as well as other factors modifying metabolism of vitamin C and function of gastric mucosa.

MATERIALS AND METHODS

31 patients were subjected to diagnostic endoscopy due to dyspepsia. Concentrations of Asc and dAsc were measured in plasma, gastric mucosa and juice with HPLC method. pH of gastric juice was determined. Histopathology examination of mucosa and urease test for Helicobacter pylori were performed. Data concerning dyspeptic symptoms and used drugs, including vitamin C preparations, were collected.

RESULTS

Patients taking vitamin C preparations had significantly lower gastric juice pH values than the others (median 2.2 vs 5.4; p < 0.01). Treatment with vitamin C preparations was also associated with higher Asc concentrations in gastric juice (median 16.6 vs. 1.8 micromol/L; p < 0.09); the difference was statistically significant in the subgroup of patients with gastritis (median 16.6 vs. 0.1 micromol/L; p < 0.04). Strong negative correlations of pH with Asc (Rs = -0.67; p < 0.001) and dAsc (Rs = -0.48; p < 0.01) concentrations were observed in gastric juice. Positive correlation of pH and relative dAsc content expressed as percent of total vitamin C concentration in gastric juice was also statistically significant (Rs = +0.48; p < 0.05).

CONCLUSIONS

Performance of the proton pump and vitamin C metabolism in the stomach are closely mutually connected. Modification of hydrochloric acid secretion may affect gastric juice vitamin C concentration. Potentially disadvantageous influence of antisecretory drugs on the mechanisms of antioxidative protection in the stomach needs further investigation.