
Melatonin
Melatonin is an indoleamine neurohormone whose levels vary in a daily cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions in animals, plants, and microbes. Many biological effects of melatonin are transduced through melatonin receptors, including the MT1, MT2, and MT3 subtypes. Melatonin also acts as a powerful antioxidant that protects lipids, proteins, and DNA against oxidative damage. Glutathione peroxidase, superoxide dismutases, and catalase are upregulated by melatonin, and melatonin scavenges free radicals as a terminal antioxidant.