The cortisol response to awakening in relation to different challenge tests and a 12-hour cortisol rhythm

Recent studies have shown that cortisol levels rapidly increase within the first 30 minutes after awakening. This response is rather robust over weeks or months and is altered by chronic stress and burnout. The present study investigated to what extent the cortisol response to awakening relates to r esponses following hCRH, ACTH(1-24), or psychosocial stress challenges in 2 2 healthy subjects. Furthermore, a 12-hour circadian cortisol profile was o btained to compare the morning response with cortisol levels obtained throu ghout the day. Results show that the morning cortisol response was of simil ar magnitude to that following injection of 1 mu g/kg h-CRH or exposure to a brief psychosocial stressor (TSST). All of these were significantly small er compared to maximal stimulation of the adrenal cortex by ACTH(1-24). Cor relation analyses revealed that the morning cortisol response was closely r elated only to the cortisol response following 0.25 mg ACTH(1-24) (r=0.63, p=0.002). We conclude that the morning cortisol response to awakening can p rovide important information on the (re)activity of the HPA axis in additio n to more 'traditional' methods like hCRH or Synacthen challenge tests. The sensitivity/capacity of the adrenal cortex appears to play a crucial role for the magnitude of cortisol responses observed after awakening.