Unravelling the role of pineal gland.

The pineal gland has been classically considered as a vestigial organ with mystic properties. With the development of new methodical experiments, its physiologic actions are unravelled vary depending on the level of the phylogenetic scale. Since the discovery of melatonin as the principal hormone of the pineal gland, is an important hormone involved in the control of circadian rhythms and other diverse biological functions. Recent metabolic, receptor and functional studies have discovered melatoninergic system(s) in living organisms, its organization, physiology and a role in some pathologic conditions. The melatonin-generating system is characterized by three basic features: (1) photosensitivity, (2) diurnal (or circadian) rhythmicity (with highest levels of melatonin production occurring at night in darkness), and (3) age-related decline in its activity.