INTERNAL DISSOCIATION OF THE CIRCADIAN MARKERS OF THE CORTISOL RHYTHMIN NIGHT WORKERS

To determine whether the circadian system of night workers is adapted to a night-active schedule, we submitted 11 night workers and 11 day-a ctive subjects to a 10-min blood sampling procedure during their usual sleep-wake cycle, permitting a precise determination of circadian and ultradian cortisol variations. In night workers, the usual shift of 8 h in the sleep period was associated with a distortion of the normal 24-h cortisol rhythm. The acrophase exhibited a shift of similar to 6. 5 h, whereas the quiescent period, abruptly interrupted by a large pea k, underwent a shift of only 3 h and lasted for similar to 5 h, as in day-active subjects. Slow-wave sleep and sleep onset occurred during p eriods of low or decreasing cortisol secretory rates, whereas awakenin gs were associated with an increase in cortisol secretory rates. These results revealed that the circadian system of night workers only part ially adapts to night work and that adaptation processes rely on an in ternal dissociation of the markers of the cortisol pattern, without di sturbing the processes that couple cortisol release and specific sleep stages.