Influence of intensity of illumination during the light period on diurnal variations of pineal indoles in rats and mice

The diurnal variations of pineal indoles in New-Zealand Black (NZB) mice and Wistar rats were determined by HPLC fluorometry. Pineal N-acetylserotonin (NAc5HT) in NZB mice showed a marked diurnal variation, but no melatonin (MLT) was detected at any time of day or night. The night-time increases of NAc5HT in NZB mice and MLT in Wistar rats were delayed about one hour in animals kept under illumination of high intensity (2000 lux) during the light period (12 h) compared with those in animals kept under illumination of low intensity (10 lux). These results suggest that the intensity of illumination during the light period affects the diurnal rhythms of pineal indoles in experimental animals.