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Serotonin

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Serotonin – A Biogenic Monoamine

Serotonin is a biogenic monoamine synthesized from the essential amino acid L-tryptophan. It is metabolized in the blood plasma, liver, and other organs. Serotonin regulates physiological processes at the cellular level by interacting with a family of cell surface receptors.
 

Serotonin in the Body

  • 80–90% of total serotonin is synthesized and stored in the enterochromaffin cells of the gastrointestinal tract (GI tract).
  • Small amounts are continuously released into the GI tract, where it stimulates peristaltic reflexes and secretion.
  • Most serotonin from the GI tract enters the bloodstream, where it is absorbed by platelets and transported to tissues. It plays roles in reproduction and tissue regeneration.
     

    Serotonin as a Neurotransmitter

  • In the central nervous system (CNS), serotonin acts as a neurotransmitter involved in regulating behavioral and physiological functions.
  • The serotonergic system (ST system) influences:
    • Memory and learning
    • Appetite and eating behavior
    • Sleep patterns
    • Temperature regulation
    • Pain modulation
    • Cardiovascular function
    • Hypothalamic regulation of pituitary hormones

  • As both a neurotransmitter and a tissue hormone, serotonin is essential for maintaining homeostasis and regulating various physiological processes in both normal and pathological conditions.

For children under 1 year: No food for 30–40 minutes before the test.
For children aged 1–5 years: No food for 2–3 hours before the test.
 

  • No food for 12 hours before the test (only water is allowed).
  • Discontinue sympathomimetic drugs 14 days before the test (as per physician’s guidance).
  • Avoid all medications 24 hours before the test (as per physician’s guidance).
  • Eliminate physical and emotional stress 24 hours before the test.
  • Do not smoke for at least 2 hours before the test.
  • Diagnosis of carcinoid tumors (neuroendocrine tumors that produce serotonin).
  • Monitoring the effectiveness of carcinoid tumor treatment.

Interpretation of Results

High Serotonin Levels

Elevated serotonin levels may indicate:

  • Metastatic carcinoid tumors of the abdomen with carcinoid syndrome (>400 ng/mL).
  • Tumors causing atypical carcinoid syndrome (e.g., bronchial small-cell carcinoma, medullary thyroid carcinoma).
  • Moderate elevation in conditions such as:
    • Dumping syndrome
    • Acute intestinal obstruction
    • Fibrocystic degeneration
    • Acute myocardial infarction
    • Tropical sprue

Low Serotonin Levels

Decreased serotonin levels are associated with:

  • Down syndrome
  • Untreated phenylketonuria
  • Parkinson’s disease
  • Severe depression
  • Werlhof disease (immune thrombocytopenia)
  • Leukemia
  • Vitamin B6 deficiency
  • Parenchymal liver disease