Vago‐vagal reflex effects on gastric and pancreatic secretion and gastro‐intestinal motility

Abstract

Pavlov (1902) in his account of the nervous regulation of digestion, stressed the importance of the discharge down the efferent vagal fibres to the abdominal viscera. This discharge he conceived as the reflex result of a 'secretory centre' in the brain stem being bombarded in the earlier stages of digestion by impulses from cephalic nerve endings, followed in the later stagesby an inflow of impulses along visceral afferent fibres in the abdominal vagus and sympathetic nerves. The importance, or even the existence, of this second type of reflex arc seemed doubtful when it was discovered that gastro-intestinal secretion and motility could, except for the cephalic reflexes, continue and be adjusted to the requirements of digestion in the absence of the extrinsic nerve supply to the abdomen (McSwiney, 1931; Alvarez, 1948). With the discovery of secretin, increasing stress was laid on the importance of hormonal control, particularly of the secretory functions of the digestive system. More recently it has been suggested that local reflexes, mediated through the intrinsic plexuses, may be concerned in hormonal release. Little attention, however, has been paid to the possibility that 'long' reflexes through the visceral afferent fibres in the vagal and sympathetic nerves to the abdomen might, by arcs through the central nervous system returning through the efferent fibres in these same nerves, play a part in regulating gastro-intestinal secretions and movements.Previous workers have attacked the problem either by studying the effects of extrinsic nerve section on the response to physiological stimulants in the lumen of the digestive tract, or by recording the secretory or motor responses to direct stimulation of the many afferent fibres, which have been shown to be present in the splanchnic nerves and abdominal vagus trunks

Vagal afferent discharge from mechanoreceptors in different regions of the ferret stomach.

“…The reason for these differences is not clear, there may have been a species difference between cat and ferret, but the most likely explanation is that both Paintal and Iggo were working with stomachs which were in an atonic state. This is suggested by the absence of spontaneous discharge in the afferent fibres, the absence of pyloric contractions which normally accompany gastric distension (Andrews et al 1979) and the absence of contractile responses which usually accompany electrical excitation of the vagus nerves (Harper, Kidd & Scratcherd, 1959;Martinson & Muren, 1963). The explanation of Paintal (1973) to account for distension of the pyloric antrum 'that contraction of the stomach starting in the body and fundus would distend the pyloric antrum thereby stimulating the endings' is not tenable in the light of subsequent research.…”

Abomasal secretion in the sheep

“…Whether these are concerned in the reflex control of gastric secretion remains to be seen but it is of interest that vagal afferents concerned with salivary secretion have already been described in the reticulo-rumen (Kay, 1958). Harper, Kidd & Scratcherd (1959) have also shown that stimulation of the central end of the abdominal vagus in the cat causes secretion of acid and pepsin in the gastric juice.…”

Impact of antral mechanoreceptor activation on the vago‐vagal reflex in the rat: functional zonation of responses.

“…For example, stimulation of vagal afferents increases acid secretion from the parietal cells, and decreases gastric pressure (Harper, Kidd & Scratcherd, 1959;Grossman, 1962;Jansson, 1969). Because these effects can be elicited by electrical stimulation of the central cut end of the abdominal vagus and are attenuated by abdominal vagotomy, these physiological responses are mediated, in part, by gastric vago-vagal reflexes (Harper et al 1959).…”