Circadian rhythms of melatonin, cortisol, and clock gene expression during simulated night shift work.
OBJECTIVE
The synchronization of peripheral circadian oscillators in humans living on atypical sleep/wake schedules is largely unknown. In this night shift work simulation, we evaluate clock gene expression in peripheral blood mononuclear cells (PBMCs) relative to reliable markers of the central circadian pacemaker.


METHODS
Participants were placed on a 10-hr delayed sleep/wake schedule simulating nighttime work followed by a daytime sleep episode.


METHODS
Baseline, intermediate and final circadian evaluations were performed in the temporal isolation laboratory.


METHODS
Five healthy candidates, 18-30 years.


METHODS
Polychromatic white light of (mean +/-SEM) 6,036 +/-326 lux (approximately 17,685 +/-955 W/m2) during night shifts; dim light exposure after each night shift; an 8-hr sleep/darkness episode beginning 2 hrs after the end of each night shift.


METHODS
Melatonin and cortisol in plasma; clock genes HPER1, HPER2 and HBMAL1 RNA in PBMCs.


RESULTS
Following 9 days on the night schedule, hormonal rhythms were adapted to the shifted schedule. HPER1 and HPER2 expression in PBMCs displayed significant circadian rhythmicity, which was in a conventional relationship with the shifted sleep/wake schedule. Changes in the pattern of clock gene expression were apparent as of 3 days on the shifted sleep/wake schedule.


CONCLUSIONS
This preliminary study is the first documentation of the effects of a shifted sleep/wake schedule on the circadian expression of both peripheral circadian oscillators in PBMCs and centrally-driven hormonal rhythms. In light of evidence associating clock gene expression with tissue function, the study of peripheral circadian oscillators has important implications for understanding medical disorders affecting night shift workers.
Centre for Study and Treatment of Circadian Rhythms, Douglas Mental Health University Institute, Montréal, Québec, Canada.
Francine O
FO
James
Nicolas
N
Cermakian
Diane B
DB
Boivin
D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D017931:DNA Primers / Q000235:genetics; D004651:Employment; D005260:Female; D015870:Gene Expression / Q000502:physiology*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood*; D014851:Wakefulness / Q000502:physiology
D017931:DNA Primers; D008550:Melatonin; D006854:Hydrocortisone