Cytokines, glucocorticoids and neuroendocrine function

Activation of the immune system is normally associated with widespread alterations in neuroendocrine activity, the profile of which depends upon the species and on the severity and duration of the stimulus. Particularly important in this regard is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis for the consequent rise in circulating glucocorticoids serves to contain the ensuing pathophysiological responses and thus to restore homeostasis. In the present study, in vivo and in vitro techniques have been used to examine the influence of various immunokines on the HPA axis and to determine whether their actions are modulated by glucocorticoids and lipocortin 1 (LC1). In vivo interleukin-1 beta (IL-1 beta), given orally or peripherally, produced increases (P < 0.01) the serum corticosterone concentration which were reversed by pretreatment with dexamethasone. IL-1 beta also produced glucocorticoid reversible increases in the release of the two corticotrophin releasing factors, CRF-41 and AVP, from the hypothalamus in vitro (P < 0.01) as also did IL-1 alpha, IL-6 and IL-8. By contrast, none of these cytokines influenced directly the release of ACTH from pituitary tissue in vitro. The inhibitory actions of the glucocorticoids on the HPA responses to cytokines observed in vivo and in vitro were mimicked by LC1 and reversed by neutralizing anti-LC1 antisera. Our results demonstrate a role of cytokines, glucocorticoids and LC1 in effecting the interplay between the brain-neuroendocrine and immune system which may be critical to host defence in conditions of both health and disease.