serotonin /ser′ətō″nin, sir′-/ [L, serum + Gk, tonos, tone] , a naturally occurring derivative of tryptophan found in platelets and in cells of the brain and the intestine. Serotonin is released from platelets on damage to the blood vessel walls. It acts as a potent vasoconstrictor. Serotonin in intestinal tissue stimulates the smooth muscle to contract. In the central nervous system, it acts as a neurotransmitter. Lysergic acid diethylamide interferes with the action of serotonin in the brain. The normal concentration of serotonin in the urine is 0.05 to 0.2 μg/mL. Also called 5-hydroxytryptamine.
