48997
document
Dark-phase light contamination disrupts circadian rhythms in plasma measures of endocrine physiology and metabolism in rats . Dark-phase light contamination can significantly disrupt chronobiologic rhythms , thereby potentially altering the endocrine physiology and metabolism of experimental animals and influencing the outcome of scientific investigations . We sought to determine whether exposure to low-level light contamination during the dark phase influenced the normally entrained circadian rhythms of various substances in plasma . Male Sprague-Dawley rats ( n = 6 per group ) were housed in photobiologic light-exposure chambers configured to create 1 ) a 12:12-h light : dark cycle without dark-phase light contamination ( control condition ; 123 μW/cm ( 2 ) , lights on at 0600 ) , 2 ) experimental exposure to a low level of light during the 12-h dark phase ( with 0.02 , 0.05 , 0.06 , or 0.08 μW/cm ( 2 ) light at night ) , or 3 ) constant bright light ( 123 μW/cm ( 2 ) ) . Dietary and water intakes were recorded daily . After 2 wk , rats underwent 6 low-volume blood draws at 4-h intervals ( beginning at 0400 ) during both the light and dark phases . Circadian rhythms in dietary and water intake and levels of plasma total fatty acids and lipid fractions remained entrained during exposure to either control conditions or low-intensity light during the dark phase . However , these patterns were disrupted in rats exposed to constant bright light . Circadian patterns of plasma melatonin , glucose , lactic acid , and corticosterone were maintained in all rats except those exposed to constant bright light or the highest level of light during the dark phase . Therefore even minimal light contamination during the dark phase can disrupt normal circadian rhythms of endocrine metabolism and physiology and may alter the outcome of scientific investigations .
48998
Intervention_Physical
Dark-phase light contamination
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Intervention_Physical
photobiologic light-exposure chambers
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Intervention_Control
light : dark cycle without dark-phase light contamination
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Outcome_Physical
plasma
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Outcome_Physical
physiology
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Outcome_Physical
metabolism
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Outcome_Physical
chronobiologic rhythms
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Participant_Condition
endocrine physiology and metabolism
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Participant_Sample-size
6 per group