Receptors, Activated by Acid, in the Duodenal Wall of Rabbits

In anaesthetized rabbits, the effect of introducing acid into the lumen of the duodenum on the frequency of action potentials in the afferent nerves was investigated. Hydrochloric acid, 0·1 and 0·05 M, and acid sodium citrate, buffered with hydrochloric acid to a pH of less than 2, induced action potentials in the distal portions of cut mesenteric nerves coming from the part of the duodenum exposed to the acid. Two types of response were noted from the upper part of the duodenum. One consisted of an intense volley of action potentials beginning almost immediately and lasting for about 15 sec. The other response was less intense; it reached its maximum in about 30 sec and lasted for periods of at least 90 sec. It is postulated that there are two types of nerve receptor in the wall of the duodenum of rabbits which may be stimulated by acid in the lumen, and evidence is presented in favour of the suggestion that the concentration of hydrogen ions is the important factor. The relationship of acid in the duodenum to inhibition of gastric secretion is discussed.