Effects of near-ultraviolet (UV-A) light on melatonin biosynthesis in vertebrate pineal gland

Biol Signals Recept. 1999 Jan-Apr;8(1-2):64-9. doi: 10.1159/000014570.


The effects of near-ultraviolet (UV-A) irradiation on nocturnal activity of serotonin N-acetyltransferase (NAT; a key regulatory enzyme in melatonin biosynthesis) in the pineal gland of the rat and chick were investigated. Exposure of the animals to UV-A during the 4th or 5th hour of the dark phase of the 12:12 h light-dark (LD) cycle suppressed the night-driven NAT activity in a time-dependent manner, the effects being generally more pronounced in rats than in chicks. The UV-A-evoked suppression of the nocturnal NAT activity was completely restored within 2 h (chicks) or 3 h (rats) in animals which, after irradiation, were returned to darkness. When a short UV-A pulse was applied to the animals after midnight, it induced a decrease in the enzyme activity in both species; yet, the effect was readily reversible only in chicks. The results presented here, as well as other data, demonstrate that UV-A light is a powerful signal affecting the pineal melatonin-generating system both in mammals and avians, and that the involved mechanisms may differ in the tested species.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chickens
  • Circadian Rhythm
  • Male
  • Melatonin / biosynthesis*
  • Pineal Gland / metabolism*
  • Pineal Gland / radiation effects*
  • Rats
  • Rats, Wistar
  • Species Specificity
  • Ultraviolet Rays*


  • Melatonin