Interactions of cytokines with the hypothalamus-pituitary axis.

Major humoral mechanisms include the endocrine and immune systems, and there is substantial literature describing interactions between these systems during infection and inflammatory processes. Within the brain, such interactions are less well known. One major brain function altered during infection and inflammation and by several endocrine hormones is sleep. These changes in sleep provide a useful illustration of the interactions between cytokines and the hypothalamus-pituitary axis (HPA). Experimental evidence is reviewed that illustrates the interaction of cytokines, especially interleukin-1 (IL-1), with the HPA in regard to their effect on sleep. The evidence linking IL-1, growth hormone-releasing hormone/growth hormone, and corticotropin-releasing hormone to sleep regulation is reviewed. There is also evidence that shows that these two major sleep-regulatory systems are linked to each other.