NCIt definition : A hormone involved in sleep regulatory activity, and a tryptophan-derived neurotransmitter,
which inhibits the synthesis and secretion of other neurotransmitters such as dopamine
and GABA. Melatonin is synthesized from serotonin intermediate in the pineal gland
and the retina where the enzyme 5-hydroxyindole-O-methyltransferase, that catalyzes
the last step of synthesis, is found. This hormone binds to and activates melatonin
receptors and is involved in regulating the sleep and wake cycles. In addition, melatonin
possesses antioxidative and immunoregulatory properties via regulating other neurotransmitters.;
Alternative definition : NCI-GLOSS: A hormone made by the pineal gland (tiny organ near the center of the brain).
Melatonin helps control the body's sleep cycle, and is an antioxidant. It is also
made in the laboratory and sold as a supplement.;
Semantic type(s)