Human gastric interdigestive
acid and
bicarbonate outputs vary cyclically in association with the migrating motor complex (MMC). These phenomena were studied in 26 healthy volunteers by constant-flow gastric perfusion, with continuous recording of pH and Pco2 in mixed gastric effluent and concomitant open-tip manometry of gastroduodenal motility. Stable
acid and
bicarbonate outputs were registered during less than 50% of the MMC cycle.
Acid secretion started to increase 71 +/- 3% into the cycle, with maximum output during
antral phase III.
Bicarbonate output increased biphasically 1) 40 +/- 5% into the cycle, coinciding with reflux of bile, and 2) at the end of duodenal phase III when the aspirate was devoid of bile. The
bicarbonate peak associated with phase III was abolished by
atropine (0.01 mg/kg iv, n = 8) and by pyloric occlusion (n = 9) but remained unchanged after
omeprazole (n = 10). The
acid peak was abolished by both
atropine and
omeprazole. It is concluded that the MMC-related changes in
acid and alkaline outputs represent two different and independent phenomena.
Acid secretion cyclicity is due to periodical variations in
cholinergic stimulation of the parietal cells. In contrast, the phase III-associated increase in
bicarbonate output is due to
duodenogastric reflux.