Corticotropin‐Releasing Hormone and Inflammation

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Abstract
Cortic otropin‐releasing hormone (CRH) is a major regulator of the hypothalamic‐pituitary‐adrenal axis (HPA) and principal coordinator of the stress response. As in stress, intracerebroventricular administration of CRH suppresses the immune system indirectly, via glucocorticoid and/or sympathetic system‐mediated mechanisms. Also, during inflammatory stress, the cytokines TNFα, IL‐1, and IL‐6 stimulate hypothalamic CRH and/or vasopressin secretion as a way of preventing the inflammatory reaction from overreacting. Recently, CRH receptors were described in peripheral sites of the immune system, and CRH was found to promote several immune functions in vitro. We demonstrated a direct role of CRH in the inflammatory immune process in vivo, by first studying the effect of systemic CRH immunoneutralization in an experimental model of carrageenin‐induced aseptic inflammation in Spague‐Dawley rats. We extended these observations to other forms of experimental inflammation, including streptococcal cell wall polysaccharide‐ and adjuvant‐induced arthritides and peptide R16 (epitope of the interphotoreceptor retinoid‐binding protein)‐induced uveitis in Lewis rats. We also studied human disease states, including rheumatoid arthritis, Hashimoto thyroiditis, and ulcerative colitis. Inflamed tissues contained large amounts of IR CRH, reaching levels similar to those observed in the hypophyseal portal system. We also demonstrated the presence of CRH mRNA and CRH receptors in inflammatory cells and identified the mast cells as a major immune target for CRH. In addition to production by immune cells, the peripheral nervous system, including the postganglionic sympathetic neurons and the sensory fibers type C, appears to contribute to IR CRH production in inflammatory sites. The production of CRH from the post‐ganglionic sympathetic neurons may be responsible for the stress‐induced activation of allergic/autoimmune phenomena, such as asthma and eczema, via mast cell degranulation. Antalarmin, a novel nonpeptide CRH receptor antagonist, displaced 125I‐labeled ovine CRH binding in rat pituitary, frontal cortex, and cerebellum, but not heart, consistent with antagonism at the CRHR1 receptor. In vivo antalarmin significantly inhibited CRH‐stimulated ACTH release and carrageenin‐induced subcutaneous inflammation in rats. Thus, antalarmin and other related compounds that antagonize CRH at the level of its own receptor have therapeutic potential in some forms of inflammation directly mediated by type 1 CRH receptors and promise to enhance our understanding of the many roles of CRH in immune/inflammatory reactions.