Background: Abnormal visceral mechanosensory and vagal function may play a role in the development of functional gastrointestinal disorders.

Aims: To assess whether vagal efferent and afferent function is linked with small intestinal mechanosensory function.

Methods: In seven patients with functional dyspepsia, six patients with a history of Billroth I gastrectomy and/or vagotomy, and seven healthy controls, intestinal perception thresholds were tested by a randomised ramp distension procedure performed with a barostat device. On a separate day, an insulin hypoglycaemia test was performed to assess the plasma levels of pancreatic polypeptide (PP) in response to hypoglycaemia, as a test of efferent vagal function.

Results: First perception of intestinal balloon distension occurred at significantly lower pressures in patients with functional dyspepsia (median 19.3, range 14.7-25.3 mm Hg) compared with healthy controls (median 26.0, range 21.7-43.7 mm Hg, p < 0.01). Sensory thresholds were significantly lower in patients after gastrectomy (median 12.2, range 8.0-14.7 mm Hg, p < 0.05 versus all others). In healthy controls and patients with functional dyspepsia, insulin hypoglycaemia significantly (p < 0.001) increased plasma PP levels. However, only two out of seven patients with functional dyspepsia had a more than twofold increase in PP values whereas all healthy controls had a more than twofold increase in PP levels after insulin hypoglycaemia (p < 0.05). In contrast, there was no significant PP response in the gastrectomised patients (median 2%, range -10 to +23%). PP responses and visceral sensory thresholds were significantly correlated (r = 0.65, p < 0.002).

Conclusions: The diminished PP response after insulin hypoglycaemia indicates disturbed efferent vagal function in a subgroup of patients with functional dyspepsia. The data also suggest that the intact vagal nerve may exert an antinociceptive visceral effect.