Gut perception in humans is modulated by interacting gut stimuli.

Digestive symptoms depend on multiple interacting gut stimuli, but integration of visceral afferent traffic is poorly understood. Our aim was to elucidate the contribution of simultaneous intestinal stimuli to conscious perception. In 17 healthy subjects, we performed stimulus-response trials of jejunal distensions (1-min duration at 5-min intervals in 8-ml increments) either alone or with a background electrical stimulus, and stimulus-response trials of electrical stimuli (1-min duration at 5-min intervals in 6-mA steps) either alone or with a background intestinal distension. The four stimulus-response trials were performed concomitantly applying the different types of stimuli in random order. Perception was measured on a scale of 0 to 6. Background stimulation markedly increased perception of test stimuli, reducing tolerance from 44 +/- 3 to 32 +/- 3 ml and from 67 +/- 6 to 33 +/- 4 mA (P < 0.05 for both). However, whereas jejunal distensions below the perception threshold did not modify perception of the background stimulus (4 +/- 1% change; not significant), unperceived electrical stimuli exerted a sensitizing effect and increased perception of the background distension up to uncomfortable levels (111 +/- 40% increment; P < 0.05). In conclusion, activation of different pools of jejunal afferents produces summative effects on perception, and this sensitizing effect can be exerted by unperceived stimulation of mechanoinsensitive jejunal afferents.