Effects of orthostasis on endocrine responses to psychosocial stress

• Plasma norepinephrine but not salivary cortisol and plasma epinephrine respond to 10 minutes standing.
• Interpretation of psychosocial stress as the only source of autonomic changes needs revision.
• Changes of endocrine markers due to psychosocial stress alone were between 25 and 82%.
• Stress exposure in a sitting position or an adequate control condition would evade this confounder.

Standardized psychological procedures have been designed to induce physiological stress responses. However, the impact of standing (orthostasis) on the physiological reaction after psychological stress remains unclear. The purpose of the current analysis was to examine and quantify the relative contribution of orthostasis to the physiological stress response by comparing a “standing with stress” to a “standing without stress” condition. We investigated the effect of standing with and without stress on responses of the sympathetic–adrenomedullary (SAM) system and the hypothalamic–pituitary–adrenal (HPA) axis using a standardized psychosocial stress protocol (Trier Social Stress Test) and a non-stress condition in a repeated measures design. Subjects (N = 30) were exposed to both conditions in randomized order and had to maintain a standing, upright position for 10 minutes. In the “standing with stress” condition, significant increases in repeatedly assessed plasma norepinephrine (NE) and epinephrine (EP), as well as in saliva cortisol were found, while in the “standing without stress” condition, no significant changes in plasma epinephrine and saliva cortisol were observed. Calculations of the relative contribution of orthostasis to physiological stress responses revealed that 25.61% of the NE increase, 82.94% of the EP increase, and 68.91% of the cortisol increase, could be attributed to psychosocial stress adjusted for the effects of orthostasis and basal endocrine output. Although these results are indicative for a marked endocrine reaction that is caused by psychosocial stress alone, our findings show that the contribution of orthostasis must be taken into account when interpreting endocrine data collected in a psychosocial stress test.