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.