Gastric HCO₃^- secretion: Relationship with Na⁺ secretion and effect of acetazolamide in humans

We examined the relationship between gastric HCO₃^- and Na⁺ secretion under fasting and sham-fed conditions in nine healthy men and also evaluated the effect of the carbonic anhydrase inhibitor acetazolamide on gastric secretion of HCO₃^- and Na⁺. Secretion of H⁺, K⁺, and Cl^- were also measured. Gastric HCO₃^- secretion rates under fasting and sham-fed conditions closely paralleled Na⁺ secretion rates. A maximally tolerated intravenous dose (10 mg/kg) of acetazolamide significantly inhibited H⁺, Cl^- and K⁺ secretion but did not significantly affect Na⁺ or HCO₃^- secretion. Thus, the gastric mucosa secretes HCO₃^- and Na⁺ in parallel in humans both under fasting and sham-fed conditions. Relative to parietal secretion of HCl, nonparietal secretion of HCO₃^- and Na⁺ is resistant to carbonic anhydrase inhibition.