Reflex changes in intestinal tone: Relationship to perception

Using an original technique, we demonstrated a modulation of intestinal tonic muscular activity (intestinal tone) by intestino-intestinal reflexes. In 11 healthy volunteers we quantitated intestinal tone variations as changes in the air volume within a flaccid bag (12 cm long) located in the proximal jejunum and maintained at a constant pressure by an electronic barostat. Validation studies with glucagon showed significant intestinal relaxation (117 ± 10% Δvol; P < 0.05). In six healthy volunteers, graded balloon distensions (1 min duration at 10-min intervals in 8-ml stepwise increments) were randomly performed 8 cm orad, 8 cm caudad, and 20 cm caudad to the bag of the barostat. Perception was scored (0-6) by a questionnaire. Distensions at the three sites induced similar perception; at the threshold for discomfort (score ≥5) distension also induced intestinal relaxatory responses (43 ± 10%, 34 ± 5%, and 32 ± 4% Δvol from orad to caudad, respectively; P < 0.05 for all). However, while unperceived orad distensions (13 ± 2 ml) induced reflex relaxation (21 ± 6% Δvol; P < 0.05), 20-cm-caudad distensions at higher levels (16 ± 2 ml, 2.7 ± 0.5 perception score; P < 0.05) did not (1 ± 7% Δvol). This dissociation between perception and intestinal tone reflexes suggests that both responses to intestinal distension are mediated by specific mechanisms.