Serotonin and enteramine both are 5-hydroxytryptamine, a monoamine neurotransmitter, and are derived from tryptophan.
About 90% of the body contains 5-HT is localized in the intestine and the rest are in platelets and the brain.
It also found in other animals and plants;
Animals: invertebrates and mollusks, arthropods, snake and bee venom/sting.
Plants: plants: tomato, pear, banana & pineapple.
Synthesis storage and destruction
It is synthesized from the amino acid tryptophan.
Tryptophan converted to 5-hydroxytryptophan with the help of enzyme hydroxylase.
5-HTP decarboxylase to produce 5-HT.
The decarboxylase is non-specific, acts on DOPA as well as 5-hydroxytryptophan (5-HTP) to produce DA and 5-HT respectively.
It is degraded primarily by MAO and to a small extent by dehydrogenase.
5-HT is actively taken up by an amine pump serotonin transporter (SERT), with a Na+ dependent carrier, which operates at a membrane of platelet and serotonergic nerve ending s (therefore, 5-HT does not circulate in free form in plasma).
This pump is inhibited by selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs).
Platelets do not synthesize 5-HT but acquire it by uptake during passage through intestinal blood vessels.
Again 5-HT is stored within storage vesicles, and its uptake at the vesicular membrane by vesicular monoamine transporter (VMAT-2).
It is inhibited by reserpine.
The enzyme MAO (especially MAO-A) metabolized 5-HT.
Musculotropic (D type) and Neurotropic (M type) – blockade by Dibenzyline (phenoxybenzamine) and Morphine.
4 Families and 14 subtypes.
The present system of classifying 5-HT receptors is based on molecular characterization and cloning of the receptor cDNAs.
5-HT receptor subtype-selective agonists or antagonists.
All are GPCRs except 5-HT3.
Decrease cAMP production
5-HT1 – Increase cAMP production 5-HT4, 5-HT6, 5-HT7
Generating IP3/DAG – 5-HT2.
The 5-HT3 is a ligand-gated cation (Na+, K+) channel which on activation elicits fast depolarization.
All subtypes of the 5-HT1 receptor couple with Gi/Go protein and inhibit adenylyl cyclase.
5-HT1A activates the K+ channel and inhibits the Ca2+ channel resulting in hyperpolarization.
These receptors primarily act as an autoreceptor in the brain and inhibit the firing of 5-HT neurons or the release of 5-HT from nerve endings.
Location of 5-HT1A receptor: Somadendritic synapse in Raphe nucleus, Brainstem, and hippocampus (antianxiety – Buspirone).
5-HT1D – Basal ganglia and substantia nigra (dopaminergic).
Hello! My name is Smrutiranjan Dash, a pharmacy professional. belonging from, Bargarh, Odisha. I have acquired Master degree in Pharmacy (Pharmacology) form B.P.U.T, Rourkela, Odisha. Presently I am working as an Assistant Professor at The pharmaceutical college, Barpali.