<<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