Endocrine Abstracts

Cortisol secretion follows a distinct circadian rhythm, with circulating levels low at sleep onset, beginning to rise between 0200 and 0400 h, peaking within an hour of waking and then declining through the day. This circadian rhythm is determined by the central endogenous clock (pacemaker) of the hypothalamic–pituitary–adrenal (HPA) axis, located in the hypothalamic supra-chiasmatic nucleus. The HPA axis plays an important role in maintaining alertness and modulatin...