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Open Access Dark-Phase Light Contamination Disrupts Circadian Rhythms in Plasma Measures of Endocrine Physiology and Metabolism in Rats

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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 W/cm2, 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 W/cm2 light at night), or 3) constant bright light (123 W/cm2). 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.

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Document Type: Research Article

Affiliations: 1: Department of Structural & Cellular Biology, Tulane University School of Medicine, Tulane, Louisiana, USA. [email protected] 2: Department of Structural & Cellular Biology, Tulane University School of Medicine, Tulane, Louisiana, USA 3: Bassett Research Institute, Cooperstown, New York, USA

Publication date: October 1, 2010

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  • Comparative Medicine (CM), an international journal of comparative and experimental medicine, is the leading English-language publication in the field and is ranked by the Science Citation Index in the upper third of all scientific journals. The mission of CM is to disseminate high-quality, peer-reviewed information that expands biomedical knowledge and promotes human and animal health through the study of laboratory animal disease, animal models of disease, and basic biologic mechanisms related to disease in people and animals.

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