The stress hormone system in various sleep disorders

Hypothalamic-pituitary-adrenal (HPA)-system activity is regulated by the suprachiasmatic nucleus, the primary endogenous circadian pacemaker. In addition, sleep plays an important modulatory role. However, data on HPA-system activity in sleep disorders are quite conflicting. A sensitive challenge test to assess negative feedback sensitivity of the HPA-system like the dexamethasone/corticotropin-releasing-hormone (DEX/CRH)-test has never been used so far in sleep disorders. Therefore we studied 25 obstructive sleep apnea (OSA) patients, 18 restless legs syndrome (RLS) patients, 21 patients with primary insomnia and compared them to 33 healthy controls. The dynamic response of the HPA-system was assessed by the DEX/CRH-test which combines suppression (dexamethasone) and stimulation (CRH) of the stress hormone system. After HPA-axis suppression the number of non-suppressors did not differ among groups indicating normal negative feedback sensitivity. In RLS patients ACTH levels were slightly lower compared to controls while cortisol levels were similar between groups. Following CRH stimulation we did not detect differences in ACTH- or cortisol levels and adrenocortical responsitivity to ACTH was comparable between groups. These results for the first time document normal HPA-system feedback sensitivity in various sleep disorders and suggest that abnormalities of the stress hormone system in affective disorders are unlikely due to concomitant sleep problems.