EFFECTS OF NEAR-ULTRAVIOLET LIGHT ON THE NOCTURNAL SEROTONIN N-ACETYLTRANSFERASE ACTIVITY OF RAT PINEAL-GLAND

Effects of near-ultraviolet (UV-A; 325-390 nm, peak at 365 nm) light o n the activity of the pineal serotonin N-acetyltransferase (NAT; a pen ultimate and key regulatory enzyme in melatonin biosynthesis) were exa mined in rats. Acute exposure of dark-adapted animals to UV-A radiatio n produced a marked suppression of NAT activity of the pineal gland, t he effect being dependent on exposure time. The decrease in the night- time NAT activity evoked by a 1-min pulse of UV-A light (as well as by a 15-s pulse of broad-band visible light) gradually deepened during t he first 40 min of treatment of animals with constant darkness, then t he enzyme activity began to rise reaching control values by 3 h. Treat ment of rats with a protein synthesis inhibitor, cycloheximide, attenu ated this night-driven reactivation of the pineal NAT activity. The pr esented results provide evidence that UV-A light is a powerful signal capable of controlling melatonin biosynthesis in rat pineal gland. (C) 1998 Elsevier Science Ireland Ltd.