ِِِAnti-serotonin Drugs

Serotonin (5-Hydroxytryptamine)
Serotonin is one of autacoids
•In human:
•90% of serotonin presents in the enterocromaffin cells in the intestine,
• 8% presents in platelets,
• 2% in CNS.
Biosynthesis:
L-tryptophan hydroxylase
L-tryptophan 5-hydroxytryptophan
Aromatic L-amino acid decarboxylase
5-hydroxytryptamine (serotonin)
•Pharmacological actions
•Nervous system:
•5-HT3 receptors in the GIT and in vomiting center in the medulla play a role in vomiting center.
•Activation of 5-HT3 receptor on vagal nerve ending causes bradycardia and hypotension.
•Serotonin, like histamine, is a potent stimulant of pain and itch sensory ending.
3-Cardiovascular system
•Serotonin causes contraction of vascular smooth muscle, through 5-HT2 receptors.
•Serotonin is a powerful vesoconstrictor except in skeletal muscle and heart where it dilate blood vessels.

A triphasic blood pressure response is seen following injection of serotonin in experimental animals:
• Initially, there is a decrease in heart rate, cardiac output, and blood pressure caused by the chemoreceptor response.
•After this decrease, blood pressure increases as a result of vasoconstriction.
•The third phase is again a decrease in blood pressure attributed to vasodilation in vessels supplying skeletal muscle.
•It can also, causes reflex bradycardia by activation of 5-HT3 receptors on chemoreceptor nerve endings.