Stress and the Nervous System

Stress has complex effects on the body's physiology. Models of stress such as hypoglycemia have identified that stress activates the hypothalamic-pituitary-adrenal (HPA) axis and sympathoadrenal system acutely. Additionally, there are delayed effects of prior exposure to hypoglycemia. The day after being exposed to a hypoglycemic stimulus there are: 1) decreases in the catecholamine release to a new hypoglycemic stress; 2) decreases in the muscle sympathetic nerve activity (MSNA) response to either a new hypoglycemic challenge or transient hypotension; 3) decreases in cardiac vagal baroreflex sensitivity (BRS); and 4) increases in sensitivity to thermal pain and altered temporal summation (decreased tolerance to a repeated minimally painful stimulus). This project will test the hypothesis that these delayed changes in autonomic nervous system function are secondary to a rise in ACTH that occurs in response to stress. Primary Aim. Infusion of ACTH (cosyntropin) will lead the next day to decreased cardiovagal baroreflex sensitivity in healthy subjects.