The Urinary 5-Hydroxyindole Acetic Acid and Plasma Nitric Oxide Levels in Irritable Bowel Syndrome: A Preliminary Study

Abstract

Background and Aims: Postprandial increase of 3-hydroxytryptamine (5-HT) has been implicated in irritable bowel syndrome (IBS). There is evidence that nitric oxide (NO) may act as a mediator of 5-HT-evoked secretions in the colon. Our aim is to investigate the role of urinary 5-hydroxyindole acetic acid (5-HIAA) and plasma NO levels (with diarrhoea) in IBS patients. Methods: Nineteen (with constipation) IBS patients (group 1), 22 IBS patients (group 2) and 18 healthy controls (group 3) were included in the study. The diagnosis of IBS was made according to the Rome I Criteria. The urine was collected for determination of 5-HIAA and venous blood was collected from each subject for the measurement of plasma NO levels. Results: The levels of urinary 5-HIAA mmol/day and plasma NO mmol/l of group 1 (22,4±2,2 and 29,4±2 respectively) were significantly higher than group 3(14,2 ± 2,3 and 21,3 ± 2,1 respectively) (p =0,036 and p =0,019 respectively). The NO level of group 1 was also significantly higher than group 2(21,8 ± 1,9) (p = 0,021). The 5-HIAA level of group 1 was higher than group 2 (15,2, ± 2,1) and the difference was marginally significant (p = 0,055). There was no difference between group 2 and group 3 with respect to 5-HIAA and NO levels. Conclusions: The results of this preliminary study lend support to the involvement of 5-HT in some symptomatology of diarrhoea predominant IBS. Furthermore, NO may be one of the effector mediators of the 5-HT-induced symptoms in these patients.