THE DISSOCIATION OF CATECHOLAMINE AND HYPOTHALAMIC-PITUITARY-ADRENAL RESPONSES TO DAILY STRESSORS USING DEXAMETHASONE

The hypothalamic-pituitary-adrenal (HPA) and sympathetic-adrenal-medul lary (SAM) systems are implicated in the human stress response. One ch aracterization of these systems is that they are nonspecific in their response, but differ in activation threshold and time course. Addition ally, they have been found to be affected commonly by strong metabolic stressors and infusions of CRH, and a hypothesis has been developed p rimarily from animal research that CRH stimulates both the HPA and SAM systems. To determine whether CRH was significantly involved in tonic as well as psychological stress-induced catecholamine levels in man, we infused 24 normal male undergraduate students with either saline (n = 12) or dexamethasone (DEX; n = 12) and evaluated their subsequent p lasma levels of ACTH, cortisol, epinephrine (EPI), and norepinephrine (NEPI). DEX produced a dramatic decrease in ACTH and cortisol levels, but no significant changes in EPI or NEPI occurred over a 4-h sampling interval. After the administration of math and speech stressors in a controlled laboratory setting, DEX inhibited the ACTH and cortisol rel ease that was noted in the saline group, but stress-induced increases in EPI and NEPI were comparable in both groups. Thus, our study sugges ts that there is a difference in the neural pathways for tonic and str ess-induced stimulation of the SAM and HPA systems.