Interleukin 1 receptor antagonist gene expression in rat pituitary in the systemic inflammatory response syndrome: Pathophysiological implications

The systemic inflammatory response syndrome (SIRS) is characterized by endothelial cell activation causing a generalized inflammatory response and cytokine-mediated pathophysiological alterations.(1-2) The pathophysiology of SIRS involves changes in the functioning of several endocrine glands, including the pituitary.(1-3) SIRS-induced alterations in pituitary function include activation of the hypothalamic-pituitary adrenal (HPA) axis causing hypercortisolemia, the euthyroid sick syndrome, and cessation of reproductive function. These changes are in part mediated by cytokines, such as tumor necrosis factor alpha (TNF-alpha) and interleukin 1 (IL-1).(4,5) IL-1 function depends on the local ratio of bioactive IL-1 and IL-1 receptor antagonist.(6,7) Here we review our studies on IL-1 beta and IL-1ra mRNA levels in the pituitary in a rat model of SIRS.(8,9) We have found that IL-1 beta mRNA peaked at 2 h after lipopolysaccharide (LPS) administration, increasing twelvefold over control values in the posterior pituitary and fivefold over controls in the anterior pituitary. IL-1ra mRNA levels peaked at 6 h post-LPS administration, later than those of IL-1 beta mRNA. IL-1ra mRNA levels increased tenfold in the anterior pituitary, but were induced only threefold in the posterior pituitary. IL-1ra gene expression is profoundly induced in the pituitary in vivo during systemic inflammation and its induction follows that of IL-1 beta, but it is differentially regulated and tissue-specific, occurring predominantly in the anterior pituitary. Future studies of the effects of IL-1 in the pituitary should take into account the local levels of IL-1ra.