Chemical stimulation of vagal afferent neurons and sympathetic vasomotor tone.

Abstract

Vagal afferents innervate a diverse range of structures of the thoracic and abdominal viscera. While a proportion of these afferents function as mechanoreceptors and respond to changes in intramural tension within the structures that they innervate, many also sense a broad range of chemical substances ranging from peptides, sugars and lipids present in the intraluminal contents of the gastrointestinal tract, as well as tissue prostanoids, cytokines and monoamines in the cardiopulmonary circulation. This review examines the effects of chemical stimulation of vagal afferents on circulatory and sympathetic vasomotor function. Notably, the von Bezold-Jarisch reflex is a cardiorespiratory reflex produced by chemical activation of cardiopulmonary vagal afferents. Classical stimulants of the von Bezold-Jarisch reflex include the Veratrum alkaloids and 5-HT(3) receptor agonists. Atrial natriuretic peptides are agents which also produce a von Bezold-Jarisch reflex-like response or a sensitisation of this reflex via an action on vagal afferents. Cholecystokinin (CCK) activates abdominal visceral vagal afferents, which apart from a clear role in mediation of satiety, also produces selective sympathetic vasomotor inhibition probably by inhibition of sub-groups of presympathetic vasomotor neurons of the rostral ventrolateral medulla. These actions of CCK may constitute a novel gastrointestinal-cardiovascular reflex. The afferent vagus transmits a diverse array of signals to the central nervous system, influencing sympathetic vasomotor and cardiomotor function, gastrointestinal function, neuroimmune function and endocrine function.