Gastric H+ and HCO3- secretion in response to sham feeding in humans.

Sham feeding (SF) was used to evaluate the effect of physiological vagal stimulation on gastric acid (H+) and bicarbonate (HCO3-) secretion in humans, as well as on parietal and nonparietal volume secretion. A recently validated method, derived from a two-component model of gastric secretion, was employed. SF increased both H+ secretion from parietal cells (P less than 0.001) and HCO3- secretion from nonparietal cells (P less than 0.01), although the H+ response was greater and more prolonged. Atropine significantly inhibited not only H+ secretion but also HCO3- and nonparietal volume secretion. Peak H+ secretion during SF averaged approximately 27 mmol/h, whereas peak HCO3- secretion averaged approximately 6 mmol/h. When H+ secretion was already maximally stimulated by an intravenous pentagastrin infusion, SF actually reduced gastric juice acidity and osmolality due to neutralization of H+ by HCO3- and to dilution of H+ by nonparietal secretions. These studies therefore indicate that vagal stimulation induced by SF increases both H+ and HCO3- secretion in humans and that this process is cholinergically dependent.