CHANGES IN GASTRIC ACID SECRETORY ACTIVITY DURING THE INTERDIGESTIVE STATE IN THE DOG

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The relationship between acid secretion, interdigestive migrating contractions (IMC) in the stomach, and gastrointestinal hormones in the dog was investigated. Heidenhain pouches and Pavlov pouches were perfused with saline (1.3 ml/min) and pH changes in the perfusate were recorded continuously by means of an indwelling pH sensor. Force transducers were used to detect contractions. The pH value started to increase 3.2min after a bolus injection of cimetidine, and decreased 3.1min after the administration of betazole hydrochloride. Seventy percent of all registered IMC cycles obtained from Pavlov pouch dogs showed a decrease in pH values from 4.2±0.1 to 1.7±0.1 (mean±S.E.) corresponding to phase II contractile activity. The other 30% of the cycles did not demonstrate any changes in pH value. Acid outputs during 10min, including the minimum pH value, were 29.9±4.6% of those observed 30-40min after feeding. The decrease in pH values during phase II was also recognized in Heidenhain pouch dogs. The serum gastrin concentration during the pH-decreasing phase (40.8±4.5pg/ml) was significantly higher (p<0.05) than that in the pH-increasing phase (23.0±3.4), and significantly lower (p<0.01) than that (141 8±10.6) obtained at 30min after feeding. The serum concentration of motilin during the pH-decreasing period (265.3±49.3pg/ml) was significantly lower (p<0. 05) than that during the increasing phase (430.8±34.3). Administration of exogenous motilin induced phase III-like contractile activity and significantly elevated the pH value from 3.9±0. 1 to 4.6 ± 0.3. Cimetidine increased pH values significantly from 4.0 ± 0.3 to 5.5 ± 0.1 (p<0. 01), and the duration of an IMC cycle (101.8±4.5min) was not significantly different from that of the control (103.5±6.5). These data indicate that a simple device used in these experiments detects changes in acid secretory activity in the canine gastric pouch within 3 min. Acid secretion during fasting is activated in association with phase II contractile activity in 70% of IMC cycles in the stomach. Gastrin and motilin are likely to be involved in controlling the activity. The H2 receptor blocker (cimetidine) suppresses acid secretion during phase II, but does not affect the IMC cycle.