24-hour melatonin and core body temperature rhythms: their
adaptation in night workers.
Weibel, L, K Spiegel, C Gronfier, M Follenius, G Brandenberger.
Laboratoire de Physiologie et de Psychologie
Environnementales/CNRS, 21 rue Becquerel, 67087 Strasbourg Cedex
APStracts 3:0373R, 1996.
In order to determine whether the melatonin (MT) rhythm is adapted to
a permanent nocturnal schedule, 11 night workers were studied during
their usual 24-hour cycle, and 8 day-active subjects during two 24
-hour cycles, once with night sleep, and once after an acute shift of
their sleep period to daytime. Rectal temperature (Tre) was
continuously recorded. In day-active subjects, the MT rhythm was not
affected by the acute shift in the sleep period, whereas the Tre
rhythm was split in a biphasic pattern with the circadian descending
phase during the night of sleep deprivation and a second descending
trend during day sleep. Night workers showed a great variability in
their MT profiles with the onset of the MT release varying between
2145h and 0505h. In contrast, the Tre rhythm was homogeneously
entrained to their usual sleep-wake cycle, with the onset of the
descending trend initiated before sleep onset so that the large fall
was seen, in some subjects, to be uncoupled with their MT increase.
The night active schedule did not induce any amplitude modification
of the Tre rhythm, as compared to day-active subjects sleeping at
night. No relationship between work-dependent factors and the extent
of the MT shift could be found. These results demonstrate the great
variability in the timing of MT secretion among night workers, in
contrast to the homogeneity of their Tre rhythm. The exact mechanisms
by which night workers adapt their circadian system are not yet
identified.
Received 12 February 1996; accepted in final form 30 September
1996.
APS Manuscript Number R87-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996