Exposure to Artificial Light at Night Alters Ultradian Rhythms in Endothelial Function.

Endogenous biological timing mechanisms are fundamental aspects of living cells, tissues, and organisms. Virtually every aspect of physiology and behavior is mediated by self-sustaining circadian clocks, which depend on light to synchronize with the external daily environment. However, exposure to artificial light at night (ALAN) can impair temporal adaptations, and affect health and disease. During a study of the effects of long-term ALAN exposure on cardiovascular function, we serendipitously detected ultradian rhythms in muscarinic receptor dependent relaxation of isolated aortic tissue. Mice exposed to dark nights displayed an ultradian pattern of maximum endothelial-dependent relaxation that was antiphase between the sexes. Rhythmic patterns of relaxation were abolished by ALAN exposure in both sexes suggesting that ALAN exposure can affect ultradian rhythms in physiology and behavior.