THE SYMPATHETIC NERVOUS-SYSTEM MODULATES PERCEPTION AND REFLEX RESPONSES TO GUT DISTENSION IN HUMANS

Background/Aims: Intestinal distention induces perception and gut refl exes via sympathetic and vagal pathways, but the modulatory mechanisms of such responses remain obscure. The aim of this study was to determ ine the effects of sympathetic nervous activity on sympathetic and vag al reflexes as well as on intestinal and somatic perception. Methods: In 9 healthy volunteers, proximal duodenal distentions were produced i n 4-mL increments and hand transcutaneous electrical nerve stimulation was produced in 3-mA increments. increasing stimuli of 1-minute durat ion were randomly performed at 10-minute intervals both with and witho ut sympathetic activation (induced by means of lower body negative pre ssure). Intestinal and somatic perception was scored by specific quest ionnaires; vagal enterogastric and sympathetic intestinointestinal rel axatory reflexes were simultaneously measured by gastric and distal du odenal barostats. Results: Sympathetic activation significantly height ened perception of intestinal distention without modifying perception of somatic stimuli (perception scores increased by 41% and -2%, respec tively). The reflex responses to duodenal distention significantly inc reased during sympathetic activation both in the stomach and in the in testine (relaxation increased by 91% and 69%, respectively; P < 0.05 f or both). Conclusions: Activation of the sympathetic nervous system se lectively increases visceral but not somatic sensitivity and enhances both vagally and sympathetically driven reflexes in the gut.