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Melatonin, an indoleamine, is a natural compound produced by various organisms, including bacteria and eukaryotes. [1] Its discovery in 1958 by Aaron B. Lerner and colleagues stemmed from the isolation of a substance from the pineal gland of cows that could induce skin lightening in common frogs.
[43] [44] Prolonged-release melatonin is safe with long-term use of up to 12 months. [11] Although not recommended for long-term use beyond this, [ 45 ] low-dose melatonin is generally safer, and a better alternative, than many prescription and over-the-counter sleep aids if a sleeping medication must be used for an extended period of time.
Melatonin receptors are G protein-coupled receptors (GPCR) which bind melatonin. [1] Three types of melatonin receptors have been cloned.The MT 1 (or Mel 1A or MTNR1A) and MT 2 (or Mel 1B or MTNR1B) receptor subtypes are present in humans and other mammals, [2] while an additional melatonin receptor subtype MT 3 (or Mel 1C or MTNR1C) has been identified in amphibia and birds. [3]
The following is a list of hormones found in Homo sapiens.Spelling is not uniform for many hormones. For example, current North American and international usage uses [citation needed] estrogen and gonadotropin, while British usage retains the Greek digraph in oestrogen and favours the earlier spelling gonadotrophin.
Melatonin is an endogenous hormone synthesized in the pineal gland in the brain involved in promoting sleep. [30] It activates both melatonin receptors MT1 and MT2 to produce beneficial effects on sleep, therefore being used exogenously for mild insomnia. [ 31 ]
The melatonin receptors are G protein-coupled receptors and are expressed in various tissues of the body. There are two subtypes of the receptor in humans, melatonin receptor 1 (MT 1) and melatonin receptor 2 (MT 2). [2] Melatonin and melatonin receptor agonists, on market or in clinical trials, all bind to and activate both receptor types. [1]
Endogenous melatonin is secreted daily in all mammals beginning after sunset and ending just before sunrise. Melatonin's chronobiotic property was initially suspected in the late 1980s when a high density of high-affinity melatonin receptors was discovered in the SCN. Little is known about the long-term effects of taking melatonin. [10] [11]
For example, melatonin, a hormonal timekeeper, is considered a strongly circadian hormone, whose secretion increases at dim light and peaks during nocturnal sleep, diminishing with bright light to the eyes. [132] In some organisms melatonin secretion depends on sleep, but in humans it is independent of sleep and depends only on light level.