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

Abstract

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.Some text books of clinical medicine, for example Bailey and Love [1968], state that there are nervous receptors in the walls of the duodenum, stimulated by a high concentration of hydrogen ions and which cause inhibition of gastric secretion. Indirect evidence in favour of such receptors is strong though it is likely that hormonal inhibitors also exist [Konturek, 1970]. Code and Watkinson [1955] reviewed the literature on the presence of nerve receptors and produced further evidence that vagal receptors are present in the dog. Hunt and Knox [1962] demonstrated that when a buffer with a low pH is introduced into the duodenum, there is a delay of gastric emptying in man, and it would seem that the concentration of hydrogen ions, acting on the receptors postulated by Code and Watkinson, provided the stimulus to delay gastric emptying. In a later paper, however, Hunt and Knox [1969] relate the effect on gastric emptying to the amount of titratable acid, rather than the pH of the gastric contents.Receptors which give rise to action potentials when stimulated by a high hydrogen ion concentration have been demonstrated in the wall of the stomach of the cat by Iggo [1957], but the definitive proofofthe presence of such receptors in the duodenum does not appear to have been published. Although it is difficult to interpret the data collected by various authors except by postulating duodenal 'hydrogen ion receptors' it seemed desirable to see whether the introduction of acid into the duodenum would result in afferent nerve impulses. A preliminary report of the study has been published [Andrews and Andrews, 1970]. METHODS Basically, the method was to introduce acid into the lumen of the duodenum and to measure the number of afferent impulses in the distal portions of cut mesenteric nerves 221

Response of Single Vagal Afferent Fibres to Mechanical and Chemical Stimulation of the Gastric and Duodenal Mucosa in Cats

“…Irrigation of parts of the gastro-intestinal tract with solutions of chemicals known to elicit reflex effects on gastro-intestinal function, will increase afferent discharge in the vagus or mesenteric nerves [Zamiatina, 1957;Sirotin, 1961;Delov, Zamiatina and Kiselev, 1960;Sharma and Nasset, 1962;and Andrews and Andrews, 1971]. These workers, using whole nerve or multifibre preparations, could provide no information on the specificities of the receptors or the quantitative features of their response.…”

Effects of Acid in Stomach and Duodenum upon the Gastric Myoelectrical Activity in Man

“…Myoelectrical activity of the antrum seems to be influenced, at least, by one of the mechanisms which control the rate of gastric emptying. Like the regulation of gastric emptying, the duodenal retro-control may be dependent upon a nervous mechanism [2], and/or upon a hormonal one. Spiking was clearly shown in afferent fibers from duodenal wall of rabbits during acidification [2] which suggests that a nervous mechanism might be involved.…”

“…Like the regulation of gastric emptying, the duodenal retro-control may be dependent upon a nervous mechanism [2], and/or upon a hormonal one. Spiking was clearly shown in afferent fibers from duodenal wall of rabbits during acidification [2] which suggests that a nervous mechanism might be involved. Acidification of the duodenal mucosa may also act through a hormonal pathway: it is the most effective stimulus of secretin release [3], This is dose-related since duodenal acidification with a solution of pH < 5 induced a pancreatic secretion which increased with the rate of the acid per fusion [15,19], Thus, it may be suggested that secretin plays a role in the hormonal control of gastric electrical activity.…”

Mechanoreceptors of the Rabbit Duodenum

“…More often an analysis of multi-unit recordings in a variety of species has been made either in vivo (Zamiatina, 1957;Sharma & Nasset, 1962;Andrews & Andrews, 1971;Itina, 1971;Andrews, Andrews & Orbach, 1972;Hardcastle, Hardcastle & Sanford, 1978, 1980 or in vitro (Sirotin, 1961;Clothier, Green, Hardcastle, Hardcastle & Sanford, 1975;Sanford, 1976). Multi-unit records do not determine whether there is selective sensitivity (specificity) of particular enteroreceptors.…”