In our ongoing studies of the hypothalmo-pituitary-adrenal (HPA) axis in SAD, we have analyzed data from a graded treadmill exercise test, which acts as a naturalistic stressor to the HPA axis. We have measured ACTH, cortisol, catecholamine, and growth hormone secretion in response to this challenge. Results suggest abnormal HPA-axis functioning in SAD patients, as evidenced by exaggerated ACTH secretion and blunted norepinephrine secretion in response to stress. These abnormalities were normalized during the summer. Our study of circadian systems has focused upon winter and summer patterns of nocturnal melatonin secretion in patients with SAD and healthy controls. These studies are reported by Dr. Thomas Wehr of the Clinical Psychobiology Branch in his report Z01 MH 02739-02 CP.
