The suppression of pineal melatonin content and N-acetyltransferase activity by different light irradiances in the Syrian hamster: a dose-response relationship.

The purpose of this study was to test the influence of various irradiances of cool white fluorescent light on the suppression of pineal N-acetyltransferase activity (NAT) and melatonin content in hamsters. Groups of animals were exposed to light irradiances ranging from 0.00-1.86 microwatts (microW)/cm2 for 20 min during the night. Both pineal NAT and melatonin were similarly depressed by the light irradiances in a dose-related manner. The shape of the resultant dose-response curves and the calculated ED50 for NAT (0.066 microW/cm2) and melatonin (0.058 microW/cm2) were remarkably similar. These findings may be relevant to the physiological control of the pineal by natural illumination.