Because the cortisol awakening response (CAR) has received increasing attention as a useful index of adrenocortical activity, the primary objective of this study was to investigate the presence of an awakening response for various salivary biomarkers of adrenocortical activity, including dehydroepiandrosterone-sulphate (DHEA-S), which acts as a cortisol antagonist, and α-amylase, which is a predictor of circulating catecholamine activity. Salivary biological indicators are considered to be valuable markers of hypothalamus-pituitary-adrenal (HPA) axis diurnal activity.
In an attempt to overcome problems associated with non-adherence to the requested sampling protocol, only young, healthy males with a physiological CAR value (defined as a 50% increase in salivary cortisol within 30 min after waking) were included in the study (67 out of 102 who initially enrolled met this criterion).
Our results suggested that, as is already known for cortisol, DHEA-S and α-amylase have significant awakening responses. In addition, daily profile of salivary cortisol, α-amylase and DHEA-S fluctuations were analysed. Significant correlations were found between salivary cortisol, DHEA-S and α-amylase levels. The results showed that cortisol and DHEA-S concentrations were inversely correlated with α-amylase levels.
This correlation confirmed the distinctiveness of the two regulatory systems: salivary cortisol and DHEA-S concentrations reflect the activity of the HPA axis, whereas α-amylase activity is more closely related to sympathetic activity. In addition, the present study emphasizes the potential value of saliva collection (which is both easy and stress-free) in monitoring changes of adrenal function, confirming that multiple sampling (especially within 1 h after awakening) is necessary to reliably characterise biomarker activity when investigating neuroendocrine changes under various conditions.