The role of serotonin in pathogenesis of unclassified irritable bowel syndrome

The pathogenesis of irritable bowel syndrome (IBS) has not been clearly understood. Numerous factors, including neurotransmitters, can interfere with the functions of the digestive tract.The aim of present study was to determine the secretion and metabolism of serotonin in patients with unclassified irritable bowel syndrome (IBS-U).The study included 50 healthy subjects (Controls) and 50 patients with IBS-U, diagnosed according to Rome IV Criteria of functional gastrointestinal disorders. The severity of gastrointestinal symptoms was assessed using the Gastrointestinal Symptom Rating Scale (GSRS- IBS). The quality of sleep was estimated by Insomnia Severity Index (ISI). The serum serotonin and melatonin levels and 5-hydroxyindoleacetic acid (5-HIAA) and 6-sulfatoxymelatonin (aMT6s) concentration in urine were determined with ELISA method.Compared to control group, patients with IBS-U had a higher serum levels (201.3 ± 37.8 vs 145.4 ± 36.9 ng/ml, p0.001) and lower levels of melatonin (5.86 ± 1,16 vs9.11 ±2.43 pg/ml, p0.001). Likewise, in IBS-U patients urinary excretion of 5-HIAA was greater, while aMT6s excretion was lower. Due to the above changes cyproheptadine (6 mg daily) or melatonin (7 mg daily) was recommended to be taken. After 12 weeks of taking cyproheptadine, the IBS symptoms disappeared in 86.6% patients, and in 20.0% of those taking melatonin. Both drugs improved sleep in equal measure.Increased serotonin secretion may be the cause of abdominal complaints in unclassified irritable bowel syndrome, what should be considered in its treatment.