MINI REVIEW
One molecule, many derivatives: A never-ending interaction of
melatonin with reactive oxygen and nitrogen species?
J. Pineal Res. 2006
Introduction
Melatonin, a tryptophan derivative, was first isolated from bovine pineal glands and was structurally identified in 1958 [1]. Subsequently, melatonin was found to be a sleep promoter [2], a chemical signal of light and darkness (Zeitgeber) as well as a regulator of photoperiod-dependent seasonal reproduction in some vertebrates. Using the fluctuating endogenous melatonin signals, vertebrates synchronize both their circadian rhythms and their circannual reproductive activities [3, 4]. Thus, the daily and seasonally changing melatonin rhythms are involved in signaling time of day and time of year and, thus, they serve as a bioclock and a bio-calendar in vertebrates [5]. Melatonin is also a potent, endogenously produced and diet-derived free radical scavenger and broad-spectrum antioxidant [6, 7]. The pineal production of melatonin in vertebrates exhibits an unambiguous circadian rhythm with its peak near the middle of scotophase and basal levels during the photophase. The amount of melatonin produced by the pineal gland of mammals changes as animals age. The tendency is that pineal melatonin production wanes
with advanced age. In humans, melatonin production not only diminishes in the aged but also is significantly lower in many age-related diseases including Alzheimer's disease [8, 9] and cardiovascular disease [10-13]. Understanding the metabolism of melatonin will help to explain the multiple functions of melatonin in organisms.