Hypertonic saline (HS) exerts various inhibitory effects on PMN function. We hypothesized that HS could inhibit transepithelial migration of PMN and thereby prevent inflammatory events in experimental colitis. Isolated human PMN were treated with HS (40 mM), and their transmigration across a monolayer of T84 epithelial cells was induced by N-formyl-methionyl-leucyl-phenylalanine. Monolayer disruption was assessed by monitoring changes in transepithelial conductance in an Ussing chamber. Colitis in mice was induced by oral administration of dextran sulfate sodium (DSS). Animals were treated with 4 or 8 ml/kg of 7.5% saline intraperitoneally two times daily for 7 days. Controls received equivalent volumes of normal saline (NS, n ϭ 6) or no intraperitoneal treatment (DSS, n ϭ 12). The severity of inflammation was evaluated based on disease activity index and histology score. HS treatment of PMN in vitro significantly reduced cell migration and the disruption of T84 monolayers compared with untreated control cells (n ϭ 5, P Ͻ 0.05). This effect of HS was dose dependent. HS treatment in vivo also reduced colitis-induced gut tissue damage, as indicated by an improved histology score compared with the NS and DSS groups. We conclude that HS inhibits transepithelial migration of PMN in vitro and gut tissue damage in vivo in a mouse model of colitis. Thus HS may have clinical value to reduce PMN-mediated intestinal damage. neutrophil activation; inflammatory bowel disease; hypertonic saline solution; inflammation; epithelium ALTHOUGH INFLAMMATORY DISEASES of the intestine are etiologically diverse, many of these diseases express similar histological features. Accumulation of neutrophils [polymorphonuclear neutrophils (PMN)] in the lamina propria is a major hallmark of the acute inflammatory response in disorders ranging from inflammatory bowel disease (IBD) to shock-induced gut dysfunction. In IBD, PMN also transmigrate from the lamina propria in the gut lumen. By measuring fecal excretion of leukocytes labeled with indium-111, migration of PMN from the circulation in the diseased intestine has been estimated to be increased by at least 10-fold in IBD patients (23). PMN are rapidly recruited from the bloodstream by cell adhesion to the vascular endothelium, transendothelial migration, and chemotaxis to the local inflammatory site. After their recruitment to such sites, PMN exert cytotoxic effects that can damage gut tissues via the release of cytotoxic mediators. A complex assortment of these cytotoxic agents, including reactive oxygen metabolites and proteolytic enzymes, is released during this inflammatory process and causes host tissue damage. In addition, PMN can further modulate such inflammatory processes by immunoregulatory functions they exert via the secretion of several important cytokines, including interleukin (IL)-1, IL-1 receptor antagonist, IL-6, IL-8, tumor necrosis factor-␣, granulocyte colony-stimulating factor and granulocyte macrophage colony-stimulating factor (15).The transepithelial migration of PMN...