Dissociation between reactivity of the hypothalamus-pituitary-adrenal axis and the sympathetic-adrenal-medullary system to repeated psychosocial stress

Objective: This study investigated endocrine and autonomic stress responses after repeated psychosocial stress. A first goal of the study was to investigate whether peripheral catecholamines and cardiovascular parameters would show similar or different habituation patterns after repeated stress. The second aim was to detect possible subgroups with regard to individual habituation patterns in the hypothalamus-pituitary-adrenal (HPA) axis and monitor their respective sympathetic stress responses. Methods: Sixty-five healthy subjects (19-45 years), 38 men and 27 women, were exposed to the Trier Social Stress Test (TSST) three times with a 4-week interval between stress sessions, Adrenocorticotropic hormone (ACTH), plasma cortisol, salivary cortisol, epinephrine, norepinephrine, and heart rates were measures repeatedly before and after each stress exposure. Results: All endocrine measures as well as heart rates increased significantly after each of the three stress sessions (F values > 16.00, all p values < .01). Although salivary free cortisol, total plasma cortisol, ACTH, and heart rate stress responses showed a significant decrease across the three stress sessions (all F values > 5.8, p < .01), no such decrease could be observed for the levels of norepinephrine and epinephrine. A cluster analysis performed on the salivary free cortisol responses to all three stress sessions revealed two response groups consisting of 30 so-called high responders and 35 low responders. The high responders also showed larger ACTH and total plasma cortisol responses compared with the low responders (all F values > 10.00, p < .01). No such differences between high and low responders could be observed with regard to catecholamine and heart rate responses. Conclusions: From these data we conclude that habituation to psychosocial stress seems to be specific for a given response system. Although HPA responses quickly habituate, the sympathetic nervous system shows rather uniform activation patterns with repeated exposure to psychosocial challenge.