The circadian system can be influenced by both the environment and human activities. For example, shift work can cause a de-synchronization between the circadian timing system in the human body and the external environment (Cuesta et al, 2014). Such disruption of regular rhythms may result in shift work-related medical problems.

Studies of simulated night shift experiments have indicated that the exposure to bright light at night for three days was able to synchronize the central clock to the inverted sleep timetable (Cuesta et al, 2014). However, more time was needed to reset the peripheral clocks that reside in the peripheral blood mononuclear cells (PBMCs).

Such observations request further explorations of the synchronizing effects on both the central and peripheral clocks. A recent study examined the sensitivity of the human central and peripheral clocks toward exogenous glucocorticoids (Cortef) given in the late afternoon (Cuesta et al, 2014). Glucocorticoids were the focus of the study because it has been associated with the circadian oscillations regulated by the central clock and the synchronizing mechanisms in rodent peripheral clocks.

The results of the study revealed higher expression of PER1 among the PBMC peripheral clocks with the oral administration of Cortef (Cuesta et al, 2014). Following six days of taking Cortef, the expression of PER2-3 and BMAL1 in PBMCs were modified by about 9.5 to 11.5 hours. However, the stages of central markers were not influenced.

The study suggested that glucocorticoids may be used to entrain the human peripheral clocks (Cuesta et al, 2014). Such finding may imply that potential interventions and synchronizing agents can be used and combined for both of the central and peripheral clocks among people including shift workers and jet-lag travelers. Further analysis would be interesting to find out what other synchronizing agents would work and the mechanisms of how they work.


Cuesta M, Cermakian N, Boivin DB. Glucocorticoids entrain molecular clock components in human peripheral cells. FASEB J. 2014 Dec 12. pii: fj.14-265686.

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