MELATONIN AS A CHEMICAL INDICATOR OF ENVIRONMENTAL LIGHT-DARK CYCLE

Melatonin (N-acetyl-5-methoxytryptamine) is an evolutionary highly con served molecule that plays an important role in conveying the clock an d calendar information to all living organisms, including man. Melaton in is synthesized in the rhythmic fashion, primarily by the pineal gla nd, and, to a lesser degree, by extrapineal tissues - namely the retin a, the Harderian gland, and the gastrointestinal tract. The rhythm of the hormone production, with maximal levels occurring at night in dark ness, is generated by an endogenous circadian clock(s) and is synchron ized with the photoperiodic environment to which animals are exposed. This brief outline surveys data on the regulation of rhythmic melatoni n biosynthesis by a circadian pacemaker and light (full spectrum white light and monochromatic lights with wavelengths both in the visible a nd invisible range). Additionally, possible applications of this chron obiotic compound in agriculture and in medicine in the treatment of ci rcadian rhythm sleep disorders are discussed.