Melatonin: Difference between revisions

melatonin is a full agonist of melatonin receptor 1 (picomolar binding affinity) and melatonin receptor 2 (nanomolar binding affinity), both of which belong to the class of G-protein coupled receptors (GPCRs).<ref name=":0">J{{cite journal | vauthors=((Jockers, R.)), ((Delagrange, P.)), ((Dubocovich, M. L.)), ((Markus, R. P.)), ((Renault, N.)), ((Tosini, G.)), ((Cecon, E.)), ((Zlotos, D. P.)) | journal=British Journal of Pharmacology | title=Update on melatonin receptors: IUPHAR Review 20 | volume=173 | issue=18 | pages=2702–2725 | date= September 2016 | issn=1476-5381 | doi=10.1111/bph.13536}}</ref> Melatonin receptors 1 and 2 are both G_i/o-coupled GPCRs, although melatonin receptor 1 is also G_q-coupled.<ref name=":0" /> Melatonin also acts as a high-capacity free radical scavenger within mitochondria which also promotes the expression of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase, glutathione reductase, and catalase via signal transduction through melatonin receptors.<ref name=":0" /><br />Melatonin is metabolized in the liver by cytochrome P450 enzyme CYP1A2 to 6-hydroxymelatonin. Metabolites are conjugated with sulfuric acid or glucuronic acid for excretion in the urine. 5% of melatonin is excreted in the urine as the unchanged drug.<ref>{{cite journal | vauthors=((Tordjman, S.)), ((Chokron, S.)), ((Delorme, R.)), ((Charrier, A.)), ((Bellissant, E.)), ((Jaafari, N.)), ((Fougerou, C.)) | journal=Current Neuropharmacology | title=Melatonin: Pharmacology, Functions and Therapeutic Benefits | volume=15 | issue=3 | pages=434–443 | date= April 2017 | issn=1875-6190 | doi=10.2174/1570159X14666161228122115}}</ref> Some of the metabolites formed via the reaction of melatonin with a free radical include cyclic 3-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), and N1-acetyl-5-methoxykynuramine (AMK).<ref name=":0" />