HPA Axis and Sleep

Sleep is an important component of mammalian homeostasis, vital for our survival. Sleep disorders are common in the general population and are associated with significant adverse behavioral and health consequences. Sleep, in particular deep sleep, has an inhibitory influence on the hypothalamic-pituitary- adrenal (HPA) axis, whereas activation of the HPA axis or administration of glucocorticoids can lead to arousal and sleeplessness. Insomnia, the most common sleep disorder, is associated with a 24hour increase of ACTH and cortisol secretion, consistent with a disorder of central nervous system hyperarousal. On the other hand, sleepiness and fatigue are very prevalent in the general population, and studies have demonstrated that the pro inflammatory cytokines IL6 and/or TNF-alpha are elevated in disorders associated with excessive daytime sleepiness, such as sleep apnea, narcolepsy and idiopathic hypersomnia. Sleep deprivation leads to sleepiness and daytime hypersecretion of IL6, whereas daytime napping following a night of total sleep loss appears to be beneficial both for the suppression of IL6 secretion and for the improvement of alertness. These findings suggest that the HPA axis stimulates arousal, while IL6 and TNF-alpha are possible mediators of excessive daytime sleepiness in humans. It appears that the interactions of and disturbances between the HPA axis and inflammatory cytokines determine whether a human being will experience deep sleep/sleepiness or poor sleep/fatigue. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG .