Abstract
The present study was aimed at further elucidating the relationship between circadian phase, rising time, and the morning cortisol awakening response (CAR). The results presented here are a secondary analysis of experimental data obtained from a study of advanced sleep-wake schedules and light exposures on circadian phase advances measured by dim-light melatonin onset (DLMO). The present results demonstrate that morning CAR is strongly related to rising time and more weakly related to DLMO phase.
Highlights
Melatonin synthesis by the pineal gland represents one circadian rhythm controlled by the suprachiasmatic nuclei (SCN) of the hypothalamus
As implied by the findings from Wilhelm and colleagues [8], the present study shows that the timing of morning peak cortisol secretion was more strongly associated with awakening than with circadian phase position, as measured by dim-light melatonin onset (DLMO) time
Burgess and Eastman [5] as well as Crowley et al [7] showed a much higher correlation between rising time and DLMO phase than was shown here. Both groups found a strong correlation between rising time and DLMO phase for subjects on unrestricted sleep schedules
Summary
Melatonin synthesis by the pineal gland represents one circadian rhythm controlled by the suprachiasmatic nuclei (SCN) of the hypothalamus. Melatonin concentrations are highest at night irrespective of the photic niche of the animal— nocturnal, crepuscular, or diurnal. Corticosteroid production by the adrenal gland exhibits a robust circadian pattern in mammals. In contrast to melatonin production, the timing of corticosteroid synthesis is closely related to the photic niche of the species, with peak levels occurring at the daily transition from quiescence to activity. The daily pattern of corticosteroid production is influenced by several interacting systems, only one of which is the master clock in the SCN. The third mechanism, influenced by the SCN, is a light-sensitive sympathetic pathway to the adrenal that is independent of the pituitary [2, 3]. Regulation of the adrenal is complex, with the multiple control mechanisms that can be differentially important to corticosteroid production, the SCN plays an important role in anticipatory corticosteroid production [4]
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