Melatonin, tryptophan function

Naturally Occurring Compounds. Many derivatives of iadole are found ia plants and animals where they are derived from the amino acid tryptophan. Several of these have important biological function or activity. Serotonin [50-67-9] (12) functions as a neurotransmitter and vasoconstrictor (35). Melatonin [73-31-4] (13) production is controlled daily by the circadian cycle and its physiological level iafluences, and seasonal rhythms ia humans and other species (36). Indole-3-acetic acid [87-51-4] (14) is a plant growth stimulant used ia several horticultural appHcations (37). 

Serotonin has been reported to function as a local antioxidant. The anti-oxidative properties of serotonin as well as of melatonin have been well documented.6 10 A discussion of the antioxidative actions of L-tryptophan and its metabolites is included in Chapter 9. 

Melatonin has been conserved evolutionarily in almost all groups of organisms from plants to protozoa to humans. It is derived from dietary sources of the amino acid tryptophan in vertebrates. It has numerous actions and functions. Increased interest in this hormone molecule has occurred in recent years, and it has been described as a master hormone and candidate for universal panacea.13 However, caution should be exercised before going overboard in regard to the overall significance of the many important activities and actions attributed to melatonin. In observing its overall and specific importance, further studies and documentation are needed. Often, such detailed analyses temper early overenthusiasm. 

Tryptamine Tryptophan Serotonine, melatonine Locan tissue animal and plant hormones (catecholamines), effect on blood pressure, intestinal peristalsis, mental functions... 

Functional end products of the essential amino acid tryptophan arise mainly through two distinctive pathways. The major pathway is degradation of tryptophan by oxidation, which fuels the kynurenine pathway (See 02011). The second and quantitatively minor pathway is hydroxylation of tryptophan and its subsequent decarboxylation to the indoleamine 5-hydroxytryptamine (serotonin) and subsequently melatonin. The metabolites of the kynurenine pathway, indicated as kynurenines, include quinolic acid and kynurenic acid. Quinolinic acid is an agonist of the NMDA receptor (see also section on glutamic acid), while kynurenic acid is a nonselective NMDA-receptor antagonist with a high affinity for the glycine site of the NMDA receptor (see also section on... 

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