definition about melatonin
Melatonin - From Wikipedia, the free encyclopedia
Melatonin, 5-methoxy-N-acetyltryptamine, is a hormone found in all living creatures from algae to humans, at levels that vary in a diurnal cycle. In higher animals melatonin is produced by pinealocytes in the pineal gland (located in the brain) and also by the retina and GI tract. It is naturally synthesized from the amino acid tryptophan (via synthesis of serotonin) by the enzyme 5-hydroxyindole-O-methyltransferase.
Many biological effects of melatonin are produced through activation of melatonin receptors, while others are due to its role as a pervasive and extremely powerful antioxidant with a particular role in the protection of nuclear and mitochondrial DNA. Melatonin is also synthesized by various plants, such as rice, and ingested melatonin has been shown to be capable of reaching and binding to melatonin binding sites in the brains of mammals.
Production of melatonin by the pineal gland is under the influence of the suprachiasmatic nucleus of the hypothalamus (SCN) which receives information from the retina about the daily pattern of light and darkness. This signal forms part of the system that regulates the circadian cycle, but it is the SCN that controls the daily cycle in most components of the paracrine and endocrine systems rather than the melatonin signal (as was once postulated). Melatonin produced in the pineal gland acts as an endocrine hormone since it is released into the blood, whereas melatonin produced by the retina and the gastrointestinal (GI) tract acts as a paracrine hormone.