New Aspects of Gastric Adaptive Relaxation , Reflex after Food Intake for More Food : Involvement of Ca ] psaicin

To accommodate the intake of food or liquid, gastric reservoir functions are important as the physiological refiex. There exist two rnajor responses as a reservoir function of the stomach ; adaptive and receptive relaxations. Adaptive reTaxation is a reflex in which the fundus of the stomach dilates in response to small increases in {ntragastric pressure when food enters the stornach. Receptive relaxation is a reflex in which the gastric fundus dilates when ('ood passes down the pharynx and the esophagus, The mechanlsms of these two types of functienal responses are to some extent clifferent, although a nitric exide CNO}dependent non adrenergic, non-cho]inergic neural pathway is involved in the both relaxation refiexes. Adaptive relaxation is an intragastric pressure-induced reflex. Stretch of the ga/stric wall activat.es the mechanoreceptors in gastric mucosa (Mu), which generate impul$es carried b}, the capsaicin-sensitive afferent sensory neuren. The sensory neuron can synapse on the inhibitory elferent neuron directly or activate it via fnterneurons of the rnyenterlc plexus. This leads to the release of NO from the nitroxergic efferent neuron, which causes relaxatien of circul'ar muscle and hence of the fundus. Alternative .y, an axon reflex causes thc NO release from the sensory neuron, resulting in hexamethoniurn-resistant gastric relaxation. Receptive relaxation is mediated by vagal motor fibers. ]n contrast with the pressure-inducecl adaptive relaxation, ganglionic nicotinic transrnission is essential in the vagally-induced relaxation. VIP and CGRP are important neurotransmil/ters ef the inhibitory sensory neuron, which, however, may not mediat,e both adaptjve and receptive relaxations. Disorders of these reservoir functions result in symptoms of early satiety and anorexia, which are the major symptoms of patients with functional dyspepsia.