Melatonin

Pronunciation

Definition 1

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. (NCI Dictionary)

Definition 2

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. (NCI Thesaurus)

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