Citric acid-enhanced Helicobacter pylori urease activity in vivo is unrelated to gastric emptying

Background: In a previous study, the use of a citric acid test meat produce d a rapid dose-dependent increase in urease activity that was significantly greater than that resulting from a pudding meal, ascorbic acid or sodium c itrate. The mechanism was hypothesized to be related to the ability of citr ic acid to delay gastric emptying and possibly to enhance intragastric dist ribution of the urea. Objective: To compare the effects of sodium citrate, two doses of citric ac id and a pudding meal on gastric motor function. Method: Eleven normal healthy volunteers were investigated using non-invasi ve techniques to measure gastric emptying and gastric motility. We evaluate d gastric emptying using the Meretek (13)Ceebiscuit solid phase gastric emp tying breath test, which employs a 340-calorie biscuit containing 200 mg of the edible C-13-blue-green alga Spirulina platensis, after the administrat ion of test meals of pudding, 2 g and 4 g of citric acid and 2 g of sodium citrate. Electrogastrograms (Digitrapper EGG) were also recorded for 30 min before and 180 min after the test meal. Results: Gastric emptying, as assessed by the half-time (T-1/2), was delaye d similarly with the pudding (136.8 +/-9 min) and with 4 g of citric acid ( 144.5 +/-7 min) (P>0.7). Sodium citrate (108.7 +/-6 min) and 2 g of citric acid (110.1 +/-6 min) had similar effects on gastric emptying (P=0.986), an d were significantly less effective in delaying gastric emptying (P<0.01) c ompared to pudding or 4 g of citric acid. The electrogastrograms remained n ormal and there were no differences among meals and no relation with the ga stric emptying results. Conclusions: The increased intragastric urea hydrolysis associated with cit ric acid test meals cannot be attributed to delayed gastric emptying. Chang es in the intragastric distribution of urea or a direct effect of citric ac id on the bacteria (e.g. via the cytoplasmic protein, UreI) are more likely to be responsible.