- * * *N -Acetyl-5-methoxytryptamine; a substance formed by the mammalian pineal gland, which appears to depress gonadal function in mammals and causes contraction of amphibian melanophores; a precursor is serotonin; m. is rapidly metabolized and is taken up by all tissues; it is involved in circadian rhythms. [melanophore + G. tonos, contraction, + -in] M. secretion is linked to both the sleep-wakefulness and light-dark cycles. Ocular perception that ambient light is dimming has been shown to trigger, via neural pathways involving the hypothalamus, increased secretion of m. by the pineal gland. Serum levels increase 10-fold just before sleep and peak around midnight. Twenty-four-hour secretion is higher in winter than in summer. The decline of m. secretion with age has been blamed for the tendency to insomnia in the elderly. Because m. acts as an antioxidant in counteracting free radicals, it has been promoted as a means of delaying aging and preventing cancer, heart disease, and Alzheimer dementia. It has also been proposed as an antidepressant because serotonin (5-hydroxytryptamine), whose metabolism is known to be disordered in clinical depression, is a chemical precursor of m.. Adequately controlled, large-scale studies of the efficacy, safety, and optimum dosage of m. are lacking. There is experimental evidence that long-term administration can reset the circadian pacemaker. Anecdotal reports suggest that shorter courses can hasten recovery from jet lag and facilitate adaptation to night-shift work. In one controlled study of 15 emergency physicians, m. did not improve sleep when subjects returned to a normal sleep pattern after working night shifts. The direct soporific effect of m. varies widely from person to person. Limited studies suggest that it may increase the duration of restful nighttime sleep in the elderly. High doses of m. result in prolonged elevation of serum m. level and increased production of prolactin by the pituitary gland. Unlike most hormones, m. is readily absorbed from the digestive tract and is a component of some foods. Hence therapeutic formulations are not subject to federal drug regulations or purity standards. Testing of commercially available preparations of m. has indicated both variation in potency and the presence of possibly harmful contaminants.
* * *mel·a·to·nin .mel-ə-'tō-nən n a vertebrate hormone C13H16N2O2 that is derived from serotonin, is secreted by the pineal gland esp. in response to darkness, and has been linked to the regulation of circadian rhythms
* * *n.a hormone produced by the pineal gland in darkness but not in bright light. Melatonin receptors in the brain, in a nucleus immediately above the optic chiasma, react to this hormone and synchronize the nucleus to the 24-hour day/night rhythm, thus informing the brain when it is day and when it is night. Melatonin is a derivative of serotonin, with which it works to regulate the sleep cycle, and is being used experimentally to treat jet lag, SADS, and insomnia in shift workers and the elderly.
* * *mel·a·to·nin (mel″ə-toґnin) a hormone synthesized by the pineal gland in many species of animals; its secretion increases during exposure to light. In adult amphibians it produces lightening of the dermal pigmentation by promoting aggregation of melanosomes. In mammals it influences hormone production and in many species it regulates seasonal changes such as reproductive pattern and fur color. In humans it is implicated in the regulation of sleep, mood, puberty, and ovarian cycles. It has been tried therapeutically for a number of conditions, including insomnia and jet lag.
Medical dictionary. 2011.
Look at other dictionaries:
melatonin — mel a*tonin n. (Physiology) A hormone secreted by the pineal gland. Chemically it is N acety 5 methoxytryptamine. Research has indicated that there are daily rhythms in secretion of melatonin, in particular due to the depressing effect on… … The Collaborative International Dictionary of English
Melatonin — Melatonin, 5 Methoxy N Acetyltryptamin, im Pinealorgan bzw. der Epiphyse nachgewiesenes, durch N Acetylierung und 5 Methylierung aus Serotonin entstehendes Hormon; bewirkt bei Fischen und Froschlurchen als Gegenspieler des ⇒… … Deutsch wörterbuch der biologie
melatonin — (n.) 1958, from Gk. melas black, dark (see MELANIN (Cf. melanin)) + ending from SEROTONIN (Cf. serotonin). So called because its secretion is inhibited by sunlight … Etymology dictionary
melatonin — [mel΄ə tō′nin] n. [ MELA(NO) + TON(IC) + IN1] a hormone, C13H16N2O2, produced by the pineal body, that lightens skin pigmentation, inhibits estrus, etc.: its secretion is inhibited by sunlight … English World dictionary
Melatonin — Not to be confused with Melanin or Melanotan. Melatonin Systematic (IUPAC) name … Wikipedia
Melatonin — Strukturformel Allgemeines Name Melatonin Andere Namen N … Deutsch Wikipedia
melatonin — /mel euh toh nin/, n. Physiol. a hormone secreted by the pineal gland in inverse proportion to the amount of light received by the retina, important in the regulation of biorhythms: in amphibians, it causes a lightening of the skin. [1955 60; <… … Universalium
Melatonin — Me|la|to|nin 〈n. 15; unz.; Biol., Med.〉 Hormon der Zirbeldrüse, das bei Amphibien zu einer Aufhellung der Haut führt u. beim Menschen an der Regulation des biolog. Zeitsinnes beteiligt ist [<Melano... + grch. tonos „Spannung“] * * *… … Universal-Lexikon
melatonin — n. a hormone produced by the pineal gland in darkness but not in bright light. Melatonin receptors in the brain, in a nucleus immediately above the optic chiasm, react to this hormone and synchronize the nucleus to the 24 hour day/night rhythm,… … The new mediacal dictionary
melatonin — melatoninas statusas T sritis chemija apibrėžtis Kankorėžinės liaukos hormonas. formulė C₈H₅N(OCH₃)CH₂CH₂NHCOCH₃ atitikmenys: angl. melatonin rus. мелатонин ryšiai: sinonimas – 3 (2 etanoilaminoetil) 5 metoksiindolas … Chemijos terminų aiškinamasis žodynas