Abolition of pentagastrin-stimulated alkaline tide using the carbonic anhydrase inhibitor acetazolamide

Background: Alkaline tide is the transient increase in blood and urine pH following stimulation of gastric acid secretion. It is attributed to HCO₃^- release from parietal cells in parallel with H⁺ secretion. The enzyme carbonic anhydrase is thought to be responsible for HCO₃^- production from CO₂^- and OH in the parietal cell. Objective: To examine the effect of pretreatment with the carbonic anhydrase inhibitor, acetazolamide, on the alkaline tide phenomenon. Methods: Ten patients with dyspepsia and demonstrable alkaline tide were tested on three separate days. The pH and base excess were determined in arterialized venous blood before and 45 minutes after an intramuscular injection of pentagastrin. The pH of the urine was measured before and 120 min after pentagastrin injection. Measurements were performed after pentagastrin alone on day 1, following pretreatment with acetazolamide 60 min before pentagastrin on day 2, and after the administration of acetazolamide alone on day 3. Results: Following the administration of pentagastrin alone, the blood base excess increased by 1.61 ± 0.2 mEq/L (mean ± standard deviation) and the calculated alkaline tide at 45 min was 33.99 ± 4.49 mEq. On day 2 with prior administration of acetazolamide, base excess decreased by 0.21 ± 0.39 mEq/L, and the calculated alkaline tide was -3.28 ± 7.57 mEq, which was significantly lower than on day 1 (P=0.0001). On day 3, following acetazolamide alone, the base excess values decreased by 0.53 ± 0.2 mEq/L and the alkaline tide was -10.05 ± 3.33 mEq; there was no significant difference compared with day 2 (P = 0.44). Conclusion: Pretreatment with acetazolamide abolished the alkaline tide induced by pentagastrin. This finding supports the view that carbonic anhydrase has a major role in the alkaline tide phenomenon.