• It is widely distributed in plants and
animals. Highest concentration in
mammals is found in the pineal gland,
acting as a precursor for melatonin. It
is synthesized from the amino acid
tryptophan and acts on several types of
1. Neurotransmitter (CNS)
2. 5-HT released from platelets may account
for vasospasm that accompanies certain
diseases like Raynaud’s.
3. Regulation of intestinal activity.
4. Synthesis of Melatonin in Pineal body.
Release of 5-HT
Release of EDRF
EFFECTS ON BLOOD VESSELS AND
• 5-HT causes constriction of renal,
splanchnic, meningeal, and pulmonary
arteries and veins and venules, but
dilatation of the blood vessels of
skeletal musles, coronaries, and skin
capillaries. It has weak direct inochronotropic
myocardium. It also stimulates smooth
muscles, especially of the intestines.
• Serotonin is widely distributed in the
CNS, serving as a neurotransmitter.
Altered functions may be responsible
for disturbances in sleep, mood, sexual
perception, migraine, temperature
psychiatric disorders and extrapyramidal activity.
I. CARDIOVASCULAR SYSTEM
1. Blood Pressure
Fall (Bezold Jarisch Reflex)
stimulation of sensory receptors in
Pressor phase:- Due to
vessels) and release of NE.
Prolonged Fall, with in 1 to 2
minutes of I/V injection.
Dilatation of B.V. in skeletal
2. Capillary Permeability:- Nil
3. Blood vessels and Hemostasis:- See Fig
4. Heart:- +ve Inotropic, +ve Chronotropic
II. SMOOTH MUSCLE
Bronchial and Intestinal smooth muscles
stimulated Bronchospasm and Increased
III. Sensory neurons
5-HT receptors located on sensory neurons
mediate a depolarizing response causing:pain, itching, respiratory stimulation,
Bezold Jarisch reflex.
Tumours of Enterochromaffin cells in G.I.T.
produce large quantities of 5-HT Diarrhaea;
Bronchospasm; Edema; Vasodilatation &
Flushing; Release of Substance P; Formation of
Excessive utilization of Tryptophan
Tryptophan Deficiency PELLAGRA
Sumatriptan is a selective agonist of 5-HT1
receptors, highly effective in treating acute
attacks of migraine. It relieves the nausea and
vomiting, but the headache may recur,
necessitating repeated administrations.
• Adverse effects include flushing and heat at the
injection site, neck pain, dizziness, and tingling
of the hands.
• The drug is contraindicated with symptomatic
hypertension as it may cause coronary
II. 5-HT ANTAGONISTS
Hypertension (α 1 blockade)
2. Methysergide (Sansert)
Prophylaxis of Migraine
3. CYPROHEPTADINE (Periactin); also
Stimulation of appetite; Smooth muscle
manifestations of carcinoid tumours.
Post-gastrectomy dumping syndrome; Cold
5. Risperidone (Blocks D2 also)
Reduction of thromboxane formation
Nausea and Vomiting associated with
Irritable bowel syndrome.
Very commonly used class of Antianxiety
and Antidepressant agents.
Like Tricyclic antidepressants, which
block NE uptake, the SSRIs block
neuronal transport of Serotonin.
Increased synaptic availability of Serotonin
stimulates a large number of Post-synaptic
5-HT receptor subtypes.
•Nausea and Vomiting
•Risk of Agitation and Restlessness
1. A patient has been diagnosed with a rare
metastatic carcinoid tumor. The neoplasm
is releasing serotonin, bradykinin and
several unknown peptides. The effects of
serotonin in this patient are most likely to
include which one of the following:
Episodes of bronchospasm
Hypersecretion of gastric acid
2. In recommending treatment for a patient
suffering from metastatic carcinoid tumors
the one least likely to be helpful is :
3. A patient undergoing cancer chemotherapy
is vomiting frequently. A drug that might
help in this situation is :
4. Which of the following is a serotonin
agonist useful for aborting an acute
migraine headache and is not derived from
a fungus :