Circulating neurotransmitter levels in irritable bowel syndrome: correlation of laboratory tests and clinical findings

Objective: to estimate blood levels of serotonin and melatonin neurotransmitters in patients with irritable bowel syndrome and to evaluate the role of neurohumoral imbalance in the development and clinical manifestations of irritable bowel syndrome phenotypes.

Materials and methods: the study included 60 patients (range, 18 – 45 years) diagnosed with irritable bowel syndrome according to the Roman IV criteria for irritable bowel syndrome (2016). 20 patients with a confirmed diagnosis of ulcerative colitis (UC) were assigned to a comparison group. The control group was composed of 45 apparently healthy subjects. All subjects were assigned to subgroups based on the prominent clinical presentation: irritable bowel syndrome with constipation (IBS-C), irritable bowel syndrome with diarrhea (IBS-D) and mixed irritable bowel syndrome (IBS-M). In addition to all the necessary procedures (clinical, laboratory and instrumental), blood concentrations of endogenous serotonin and melatonin were measured using enzyme-linked immunosorbent assay (ELISA).

Results: the concentrations of endogenous serotonin and melatonin were significantly lower in patients with irritable bowel syndrome as compared with those having ulcerative colitis or healthy individuals. The detection rates of lowering serotonin levels were 53.3 % and 65 % — for melatonin. Low levels of melatonin were detected both in IBS-D and IBS-C patients. 69.57 % of IBS-D patients had elevated levels of serotonin as compared with the reference values for healthy subjects. We found a strong correlation between the severity of bloating and abdominal pain on the one hand, and low levels of endogenous serotonin and melatonin, on the other hand.

Conclusion: our findings suggest that serotonin and melatonin neurotransmitters play a significant role in the pathophysiology and clinical manifestations of estimate blood levels of serotonin and melatonin neurotransmitters in patients with irritable bowel syndrome.

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