Near-ultraviolet radiation suppresses pineal melatonin content.

UV radiation (200-400 nm) is generally considered to be outside the range of visible illumination for mammals. The aim of this study was to determine if UV wavelengths can influence pineal physiology. Experiments on hamsters confirm that wavelengths as low as 305 nm are transmitted through the clear ocular media to the retina. Furthermore, low irradiances of broadband (340-405 nm) and monochromatic (360 nm) UV radiation are capable of suppressing high nocturnal levels of pineal melatonin in intact, but not blind, hamsters. These data indicate that the hamster eye and neuroendocrine system are able to detect and respond to near-UV wavelengths.