<<Disclaimer: Verify this information before applying it to your situation.>>

Here is a description for Serotin, don't know if this is what you are looking
for:  A chemical, 5-hydroxytryptamine (5-HT), present in platelets,
gastrointestinal mucosa, mast cells, and carcinoid tumors.  Serotonin is a
potent vasoconstrictor.  It is also a neurotransmitter in the central nervous
system and is important in sleep-waking cycles.  Are you more interested in
looking for information on carcinoid syndrome?

Hope this helps you.  Good luck.

Clelia