We examined the presence and potential role of local corticotropin-releasing hormone (CRH) in experimental uveitis in rodents. This 41-amino acid peptide, originally isolated from the hypothalamus, is also secreted locally in experimentally induced and natural inflammatory sites, where it exerts autocrine or paracrine proinflammatory effects. Female Lewis rats were immunized with the major pathogenic epitope (R16 peptide) of the interphotoreceptor retinoid-binding protein in complete Freund's adjuvant, monitored daily, and killed 8, 9, 10, 12, 14, or 18 days later, after having developed uveoretinitis. Immunoreactive CRH (IrCRH) was detected by immunohistochemistry in the uveitic eyes in the cytoplasm of inflammatory cells (macrophages, lymphocytes, and polymorphonuclear cells) infiltrating the iris, ciliary body, vitreous, retina, and choroid depending on the stage of the disease. The intensity of the IrCRH staining was positively correlated with the severity of the disease based on morphological criteria. The amount of IrCRH measured by RIA varied between 0.18 +/- 0.03 (mean +/- SE) and 0.79 +/- 0.07 pmol/g wet tissue (8th and 14th day of the disease, respectively). Ophthalmic IrCRH in uveitic rat eyes had similar chromatographic mobility as rat/human CRH-(1-41) by HPLC. Furthermore, female B10.A mice were immunized with interphotoreceptor retinoid-binding protein and treated during the induction (0-7 days) or expression (8-16 days) stages of the disease with ip injections of the anti-CRH antibody TS-2 or placebo nonimmune rabbit serum. The early anti-CRH treatment significantly decreased the disease intensity compared to that in placebo- or late-treated animals (P < 0.05, by analysis of variance). We conclude that IrCRH is present at the site of inflammation in rodent experimental uveitis and that its expression correlates with the natural history and intensity of the disease. Immune CRH appears to play an early pathogenetic role in the induction of experimental uveitis.