AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 1 261-R267, Copyright © 1993 by American Physiological Society
The circadian melatonin and cortisol secretion pattern in permanent night shift workers
M. Roden, M. Koller, K. Pirich, H. Vierhapper and F. Waldhauser
Division of Clinical Endocrinology and Diabetes Mellitus, University of Vienna, Austria.
In permanent night shift workers the impact of environmental time cues on
the circadian system is conflicting. Rhythm adjustments to the nocturnal
work schedule have been described, and their significance for tolerance to
shift work is under discussion. Reports concerning the effect of this work
situation on the setting of the endogenous clock are, however,
inconsistent. We examined nine healthy young male permanent shift workers
with high work satisfaction at the end of a week on night work and seven
male controls with normal diurnal working hours. All subjects were admitted
to a research facility for 28 h, and blood was collected with a
continuous-withdrawal pump in portions taken hourly for the estimation of
the circadian melatonin (MT) and cortisol secretion pattern. One control
did not exhibit a circadian secretion pattern. When compared with the other
controls (n = 6), all except one of the shift workers showed no difference
in the phase or phase relationship of their hormonal profiles. In the shift
workers, a minor trend toward elevation of the MT amplitude and an increase
in two indicators for the amount of MT secreted were noticed. One
individual displayed inverse hormone rhythms with an undisturbed phase
relationship of MT and cortisol and inconspicuous hormone amplitudes. He
showed, however, an inverse day-night rhythm in his private life, too. The
data collected suggest that even permanent night workers with a high degree
of work satisfaction do not usually lose the diurnal orientation of their
endogenous clock. Factors other than reorientation of the circadian system
may be more important for high tolerance to shift work.
