Control of the Antral Motor Response to Feeding by Gastric Acid Secretion in Rats

1. The motor response of the antrum to feeding was examined in relation to gastric acid content in six adult rats fitted with electrodes and strain gauges on the antrum, two of them also having a small cannula in the fundus. 2. After fasting overnight, feeding was accompanied by an immediate increase in antral activity of seventeen to nineteen strong contractions lasting 5.33 +/- 1.15 min. Both the duration and amplitude of this antral motor response were increased 2 hr after ingestion of cimetidine (20 mg/kg) or 60 min after intramuscular administration of the same dose of proglumide. 3. By contrast, the response to feeding was reduced by 43% in duration and by 58% in amplitude during an intravenous infusion of pentagastrin (5 mg/kg per hr) and disappeared after an infusion of HCl into the stomach. The area under the curve of the pressure developed by the gauge, used as a motility index, was nearly doubled when the pH of the gastric contents increased from 3.1 to 5.7 and was halved when the pH decreased from 3.1 to 2.2. 4. In normal or inhibitory gastric acid secretion, the blockade of the antral motor response to feeding appeared when the total acid content of the gastric juice reached 35-70 mu equiv/ml. 5. The results indicated that the rate of gastric secretion is of paramount importance in regulating the magnitude of the antral motor response to feeding. It is suggested that the vagally stimulated antral motility is rapidly counteracted by the increased acid secretion.