The purpose of this study was to examine how the physical characteristics of light influence the short photoperiod-induced atrophy of the reproductive system. In the first experiment, groups of Syrian hamsters were exposed to a 14-h light, 10-h dark (14:10) photoperiod, a 11:13 photoperiod or a 11:13 photoperiod extended by 3 h of light at an irradiance of 20, 2, 0.2, 0.02, or 0.002 μW/cm2. Animals in the 11:13 photoperiod and the 11:13 photoperiod extended by 0.02 and 0.002 μW/cm2 underwent reproductive regression, as evidenced by decreased testicular and accessory sex organ weight and pituitary PRL levels. In the second study, groups of hamsters were exposed to a 14:10, 11:13, or 11:13 photoperiod extended by 3 h of red, yellow, green, blue, or near-UV light at 0.2 μW/cm2. Animals in the 11:13 and the 11:13 photoperiod extended by red or yellow light underwent reproductive atrophy. These results demonstrate that light irradiance and wavelength are important determinants of the photoperiodic regulation of the Syrian hamster reproductive system.
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