[Melatonin--the hormone of darkness]

Melatonin is a hormone produced mainly by the pineal gland during the dark phase of the circadian cycle with typical circadian rhythm with maximal secretion at night and depression during the day. The indoleamine has wide regulatory and integrative functions. Perhaps there is no organ and system which can escape the influence of epiphysis, incl. reproductive, cardiovascular gastrointestinal, respiratory as well as renal system and water and mineral metabolism. Melatonin regulates not only neuroendocrine functions but also has immunoenhancing and antitumor effects. That is why there are trials/attempts these properties to be utilized in the treatment of malignancies and AIDS patients. The hormone plays a certain role in temperature regulation in mammals as well as in the onset of puberty and senescence. Attention has been paid to its role as a scavenger of toxic free radicals and it is believed that melatonin is the most effective lipophilic antioxidant. However, the exact mechanism of action of this high active hormone remains to be elucidated. Further studies are also necessary for discovering the next its properties and functions.