Continuous Measurement of Gastric Bicarbonate Secretion in Man under Basal Conditions and after Sham Feeding

Abstract

The mucous cells in the gastric epithelium actively secrete bicarbonate into the mucus layer, which is adherent to the surface of the mucosa. The presence of a pH gradient in the mucous gel layer indicates that the mucus-bicarbonate barrier is a first line of defence against acid. Modified sham feeding with the chew and spit technique evokes a physiological vagal stimulation of acid secretion in man. The aim of the study was to determine whether the gastric bicarbonate secretion in man is also under vagal control. A computerised measuring system for continuous determination of pH and pCO2 was utilised. The measuring device with pH and pCO2 electrodes, was coupled between the aspiration outlet of a Salem sump tube and an Egnell suction pump. The bicarbonate concentration was calculated every 30th seconds by a computer throughout the experiment from the sum of free bicarbonate according to the formula of Henderson-Hasselbalch and the CO2 concentration from the pCO2, representing free bicarbonate which has reacted with hydrogen ions. After an overnight fast the subjects were given cimetidine. The gastric tube was positioned in the antrum and physiological saline containing phenol red (8mg/l) was infused at a constant rate of 440 ml/15 min through an additional tube into the proximal stomach. The saliva was continuously aspirated. Duodenogastric reflux was identified as a sudden and rather short-lived spike of bicarbonate output and was omitted in the calculation of gastric bicarbonate secretion. After measurement of basal bicarbonate secretion the subjects were given a meal of hamburger and omelette, which they chewed and spat out during 15 minutes. The basal gastric bicarbonate secretion in six subjects was 317 ± 58 μmol/h (mean ± SEM) and increased during and after sham feeding to 649 ± 169 μmol/h (p < 0.05). The mean pH, mean pCO2 and HCO3 output under basal (B) conditions and during sham feeding (S) in one subject was indicating that the increase in bicarbonate secretion following vagal stimulation with sham feeding was not secondary to increased luminal acidity as the pH level was not substantially lowered during or after sham feeding.

Key Words:

• Gastric bicarbonate secretion
• humans
• vagus nerve
• sham feeding