Serotonin (5-HT) is synthesized from tryptophan and is found in the intestine, platelets, and brain. It is stored in nerve endings and platelets then released and reabsorbed by serotonin transporters. There are multiple types of serotonin receptors which mediate its various actions in the cardiovascular, gastrointestinal, respiratory, and central nervous systems. Serotonin can both constrict and dilate arteries, stimulate smooth muscles and peristalsis, inhibit gastric acid and protect ulcers, and cause pain sensations and hyperventilation when activated.

1. OPTOM FASLU MUHAMMED

2. 5-HYDROXYTRYPTAMINE
( 5-HT, Serotonin)
-90% : localized in intestine
-rest : platelets and brain.
-also found in plants : banana, pear, pineapple, tomato.

3. STORAGE, SYNTHESIS & DISTRIBUTION
- It is synthesised from amino acid tryptophan.
- degraded primarily by MAO and to a small extent by
dehydrogenase.
- 5-HT is actively taken up by an amine pump serotonin
transporter (SERT), a Na+ dependant carrier, which
operates at the membrane of platelets and serotonergic
nerve endings.

4. - This is inhibited by selective serotonin reuptake inhibitors
(SSRIs)

5. SEROTONIN RECEPTORS
- Based on pharmacological criteria :
- musculotropic ( D type)
- neurotropic ( M type)
- 5 HT receptor types : ( 5 HT1, 5 HT2, 5 HT3, 5 HT4 etc..)

6.  ACTIONS
- CVS :
arteries are constricted (by action on smooth muscle ) as
well as dilated (through EDRF release) by direct action
of 5-HT.
- SMOOTH MUSCLES
Potent stimulator of g.i.t both by direct action as well as
through enteric plexuses.
5HT containing neurons may regulate peristalsis

7.  GLANDS
- inhibits gastric secretion ( both acid and pepsin)
- Ulcer protective property
- NERVE ENDINGS AND ADRENAL MEDULLA
- Afferent nerve endings are activated – tingling and
pricking sensation, pain.
-

8.  RESPIRATION
- stimulation of respiration and hyperventilation.
 PLATELETS
- cause change in shape of platelets
- It’s a weak aggregator of platelets- at the site of injury

9.  CNS
- given i.v, it does not produce central effects because it
poorly crosses blood brain barrier.
- It’s an inhibitory transmitter.
- Direct injection in the brain produces sleepiness, changes
in body temperature, hunger and a variety of behavioral
effects.

10. 5 HT receptor agonists
 D-lysergic acid diethyl amide (LSD)
 Azapirones
 Sumatriptan
 Cisapride

11. 5-HT ANTAGONISTS.
 CYPROHEPTADINE
-CLOZAPINE
RISPERIDONE
ONDANSETRON