A demonstration of bicarbonate production by the normal human stomach in vivo.

Bicarbonate secretion by the stomach may play a role in gastric mucosal protection, and we have therefore examined bicarbonate secretion in the human stomach. Gastric bicarbonate production and contamination with salivary and duodenal bicarbonate was measured in healthy volunteers using an intubation technique. The stomach and duodenum were perfused with nonabsorbable markers and the pH, PCO2, marker, and amylase concentrations measured in 10-min gastric and duodenal aspirates. These measurements enabled calculation of gastric bicarbonate content and the amount of bicarbonate contributed by saliva and duodenogastric reflux. Acid secretion was suppressed by intravenous cimetidine. Validation studies demonstrated a good correlation between instilled and calculated recovered bicarbonate (r = 0.97, P less than 0.001, N = 6), and marker recovery was consistent in each subject. Over a 6-h period, gastric pH ranged from 6 to 7 and PCO2 from 20 to 40 mm Hg. Gastric bicarbonate output stabilized at 326--392 mumol/hr and mean bicarbonate concentration ranged from 2.3 to 20.0 mmol/liter. Approximately two thirds of this bicarbonate was free, 11% was derived from duodenogastric reflux, and 3% from swallowed saliva. This study demonstrates secretion of bicarbonate by the human stomach in vivo at a rate equivalent to 10--20% of basal acid secretion.