ABSTRACT
The circadian production of melatonin and rhythms of associated enzymes in the pineal gland of mammals have long been known to be regulated by the prevailing light-dark environment. The current survey is concerned with the 24-h pattern of melatonin production in the mammalian pineal gland and how it is altered by the imposition of light or nonvisible portions of the electromagnetic spectrum during the night when the production of the ubiquitously acting pineal hormone is normally elevated. Besides light brightness or intensity being a critical factor in the suppression of pineal melatonin production, the specific wavelength of light to which animals are exposed is also important. Hydroxyindole-O-Methyl Transferase is generally considered rather unresponsive to the lighting environment and, therefore, the activity of this enzyme likely is not an ideal index to use to assess the inhibitory effects of different wavelengths of light on pineal melatonin formation.
