INGESTION, GASTRIC FILL, AND GASTRIC-EMPTYING BEFORE AND AFTER WITHDRAWAL OF GASTRIC CONTENTS

The notion that satiation signals are derived from the stomach with no additional contribution of postgastric sources (J. A. Deutsch. In: Handbook of Behavioral Neuroscience. Food and Water Intake. 1990, vol. 10, p. 151-182) was evaluated in two experiments. In experiment 1, the gastric contents were withdrawn after the rat met the satiety criterion for an initial intraoral intake test(12.5% glucose delivered at 1.0 ml/min). Ten minutes later, the intraoral infusion was continued until the rat again met the satiety criterion. We found that rats reingested an amount closely corresponding to the amount withdrawn, in agreement with previous studies using spout-licking tests. Despite a lower gastric emptying rate during reingestion than during the initial test, the amount recovered from the stomach (both volume and solute content) after reingestion was significantly less (gastric volume 16% less; gastric glucose 18% less) than that withdrawn initially. In experiment 2, a portion (8 ml) of the gastric contents was removed after the end of an initial intraoral intake test and, after 10 min, rats were again given an opportunity to ingest to satiety. The procedure was repeated for a total of,three withdrawals (24 mi) and three reingestion opportunities. Rats accurately replaced the amounts withdrawn such that net intake at the end of the experiment did not differ from that ingested during the initial test. In addition, the amount recovered from the stomach after the terminal test was considerably less (gastric volume 25% less; gastric glucose 29% less) than that recovered at the end of single-test control sessions. Both experiments show that gastric feedback cannot alone account for the termination of intraoral intake. The results suggest that rats defend total intake and do so via the integration of signals derived from postgastric as well as gastric sources.