MECHANISMS BEHIND CHANGES IN GASTRIC-ACID AND BICARBONATE OUTPUTS DURING THE HUMAN INTERDIGESTIVE MOTILITY CYCLE

Human gastric interdigestive acid and bicarbonate outputs vary cyclica lly in association with the migrating motor complex (MMC). These pheno mena were studied in 26 healthy volunteers by constant-flow gastric pe rfusion, with continuous recording of pH and PCO2 in mixed gastric eff luent and concomitant open-tip manometry of gastroduodenal motility. S table 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 ou tput increased biphasically 1) 40 +/- 5% into the cycle, coinciding wi th reflux of bile, and 2) at the end of duodenal phase III when the as pirate 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 oc clusion (n = 9) but remained unchanged after omeprazole (n = 10). The acid peak was abolished by both atropine and omeprazole. It is conclud ed 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 parieta l cells. In contrast, the phase III-associated increase in bicarbonate output is due to duodenogastric reflux.