Imipramine decreases oesophageal pain perception in human male volunteers

Background-Visceral hyperalgesia is a hallmark of functional gastrointestinal disorders. Antidepressants improve symptoms in these patients, although their mode of action is unclear. Antidepressant, anticholinergic, and analgesic mechanisms have been proposed. Aims-To investigate whether imipramine, which has a visceral analgesic effect, increases pain thresholds to experimental visceral pain. Methods-Visceral perception for first sensation and pain was measured with intraoesophageal balloon distension in 15 male volunteers. The effect of imipramine was studied in a double blind, placebo controlled, crossover study. Imipramine was given in ascending doses for 12 days (25 mg days 1-3, 50 mg days 4-6, 75 mg days 7-12), with oesophageal perception studied on day 13. Results-Inflation volumes and intraballoon pressures at first sensation were not different between placebo and imipramine. Balloon inflation volume at pain threshold was higher on imipramine (p=0.015). Median intraballoon pressures were not different at pain threshold for placebo and imipramine. Oesophageal wall compliance was not affected by imipramine. Conclusion-Increased pain thresholds on imipramine in this group of normal male volunteers in the absence of changes in oesophageal tone imply the presence of a visceral analgesic effect.