Gastric emptying and secretion in the rhesus monkey.

The volume and composition of the gastric contents as well as the rates of gastric emptying and secretion were determined simultaneously in conscious chair-adapted monkeys. These determinations were made during fasting and after a liquid meal, thereby allowing studies of the physiologic variables which regulate gastric emptying and gastric secretion. Administration of a water meal is followed by a complex pattern of changes in rates of secretion as well as the fractional rate of emptying. During administration of a 100-ml water meal (pH 7.4), intragastric volume increased while acid concentration decreased; both then returned to fasting values 50 min later. The fractional rate of emptying increased fivefold during administration of the water meal, returned to basal values after 30 min, and then increased again, indicating that gastric emptying cannot be characterized as a simple first-order process with a constant coefficient. The pattern of the change in the rate of water secretion was similar to that for fractional gastric emptying. In contrast, after the meal, gastric acid secretion increased steadily and did not become maximal until 20 min.