| (enteramine, thrombocytin), a local vasoconstrictor (5-hydroxytryptamine) and general hypotensive agent synthesized from tryptophan and found in tissues, rather than being transferred by blood to sites of action. Most serotonin in mammals is found in the gastrointestinal tract, although the kidney, liver, and brain also produce it. It is absorbed by platelets from the site of tissue damage, where it aids hemostasis locally by vasoconstriction and systemically by reducing blood pressure. |