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 (μW)/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 μW/cm2) and melatonin (0.058 μW/cm2) were remarkably similar. These findings may be relevant to the physiological control of the pineal by natural illumination. (Endocrinology 113: 293, 1983).
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