Motility-related cyclic fluctuations of interdigestive gastric acid and bicarbonate secretion in man. A source of substantial variability in gastric secretion studies.

The relationship between interdigestive gastric motility and secretion was studied in eight healthy volunteers. Acid and bicarbonate output rates were measured with a high time resolution, using a perfusion system based on continuous registration of pH and PCO2 of gastric effluent. Antral pressure was measured by manometry. The total duration of the interdigestive motility cycle (time between two phase-III complexes) was 96 +/- 12 min (mean +/- SE). In late migrating motor complex phase II, acid output, bicarbonate output, and bile reflux increased significantly. Acid secretion reached a peak in association with motor phase III. The gastric lumen was then rapidly alkalinized; this phenomenon was due to a simultaneous decrease in acid secretion and a short-lasting (15 +/- 2 min, mean +/- SE) phasic increase in bicarbonate output, which was not associated with bile reflux (bilirubin). After these phase-III-related events both acid and bicarbonate output rates reached a relatively stable level during phase I and early phase II. This period of stability constituted 47 +/- 3% (acid) and 41 +/- 6% (bicarbonate, means +/- SE), respectively, of the cycle. The peak to base line output ratio was 6.6 +/- 1.2 (p < 0.001) for acid and 2.8 +/- 0.3 (p < 0.001) for bicarbonate (means +/- SE). The results show a marked variability in acid and bicarbonate output rates during the interdigestive motility cycle. The magnitude of this variability has previously been underestimated owing to poor time resolution of the secretion measurements. If not taken into account, these 'spontaneous' secretory variations may constitute a considerable source of error in gastric secretion studies.