Melatonin Melatonin, or 5-methoxy-N-acetyltryptamine, is a hormone produced by pinealocytes in the pineal gland, located in the brain, but also in the retina and GI tract. It is a derivative of the amino acid tryptophan. Melatonin produced in the pineal gland acts as an endocrine hormone since it is released into the blood. On the other hand, melatonin produced by the retina and the GI tract is considered a paracrine hormone. Melatonin helps regulate sleep-wake or circadian rhythms. Normally, production of melatonin by the pineal gland is stimulated by darkness and inhibited by light. Melatonin can suppress libido by inhibiting secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the anterior pituitary gland -- especially in mammals that have a breeding season when daylight hours are long, such as sheep. Nobel Prize laureate Julius Axelrod performed many of the seminal experiments elucidating the role of melatonin and the pineal gland in circadian rhythms. Beta blockers decrease nocturnal melatonin release. Melatonin is synthesized by various plants such as rice and ingested melatonin was shown to be capable of reaching and binding to melatonin binding sites in the brain of mammals. In recent times, melatonin has become available as a drug and a dietary supplement. It appears to have some use against insomnia and jet lag. Melatonin is a powerful antioxidant which can easily cross cell membranes. It has been studied for the treatment of cancer, immune disorders, cardiovascular diseases, depression, seasonal affective disorder, and sexual dysfunction; no apparent benefit in these has been found. To synthesize melatonin, serotonin is converted to N-acetylserotonin by the enzyme 5-HT N-acetyltransferase. N-acetylserotonin is then converted to melatonin by the enzyme 5-hydroxyindole-O-methyltransferase. See serotonin for details on how tryptophan is converted to serotonin. Melatonin has been shown to increase the lifespan of mice by 20% in some studies

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