AUTOCOIDS AND ANTAGONISTS-Contd...
SEROTONIN AND IT'S ANTAGONISTS
Serotonin a central nervous system stimulating hormone found in the CNS neurons was already discussed in this blog as CNS stimulants. But in addition, to being as a neuronal biochemical this hormone is present in each and every cell of our body tissue as an autocoid without being secreted into the blood system directly.
Chemically it is a derivative of tryptamine with a hydroxyl ion at the 5th position.
Of course tissue serotonin is not secreted into the blood but blood platelets are containing serotonin.90% of the body's serotonin are present in blood platelets and the enterochromaffin cells of the digestive systems.
Pharmacologically serotonin is known as a hormone of ecstasy and pleasure, and a low level of it produces sadness. The body synthesizes serotonin from the aminoacid L-tryptophane and a good supply of food enriched with L-tryptophane serves as
antidepressants.
Sesame seeds are rich in L-Tryptophane.
Serotonin is acting through its seven major types of 5-HT receptors subtypes.
Serotonin is mostly metabolized by mitochondrial monoamine oxidase enzymes.
Physiology
1.Neurotransmission
2.Regulation of pituitary functions(as an autocoid)
3.General vasoconstriction except for skeletal muscle and heart where it causes vasodilation(as an autocoid)
4.Contraction of GI smooth muscle(as an autocoid)
5.Stimulation of pain receptors(as an autocoid)
6.Precursor to melatonin
Sumatriptan an antimigraine drug is the serotonin agonist
Sumatriptan has side effects of dizziness, muscle weakness, and neck pain.
Antagonists
1.Ketanserin that lowers blood pressure
2.Ondansetron is used to relieve nausea and vomiting in post-surgical procedures and chemotherapy.
3. Cyproheptadine is used to treat smooth muscle contractions.
The above antagonists also block H-1 and alpha receptors.
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