Background: Irritable bowel syndrome (IBS) is generally considered to have a psychogenic component in its physiopathology.
Aim: To study the role of serotonin (5-hydroxytryptamine; 5-HT), monoamine oxidase (MAO) and anxiety, and to elucidate the relationship between these in patients with diarrhea-predominant IBS.
Methods: 5-HT and MAO activity and anxiety levels were studied in 20 healthy volunteers (aged 18-25 years; all men) and 57 patients with diarrhea-predominant IBS (30-60 years; all men).
Results: The concentrations of 5-HT (0.3 [0.04] microg/ mL) and MAO (15.5 [3.2] U/mL), and the anxiety level score (14.4 [2.9]) were significantly higher (p < 0.001) in patients than in healthy volunteers (0.1 [0.02], 6.4 [1.4] and 3.4 [1.2], respectively). These parameters correlated with each other in both patients and volunteers.
Conclusions: Elevated 5-HT and MAO activity and anxiety may play a role in patients with diarrhea-predominant IBS.