PURPOSE:To clarify whether endogenous peroxisome proliferator-activated receptor gamma (PPARgamma) and its ligand, rosiglitazone, affect retinal leukostasis and the associated vascular leakage using an experimental diabetic model. METHODS:Diabetes was induced in heterozygous PPARgamma+/- mice and Brown Norway rats with an intraperitoneal streptozotocin (STZ) injection. Retinal leukostasis and leakage, quantified by concanavalin A (Con A) lectin perfusion labeling combined with a fluorophotometric dextran leakage assay, were investigated at 120 days in diabetic PPARgamma+/- and wild-type mice and at 21 days in diabetic rats receiving rosiglitazone or the vehicle. The retinal protein expression levels of vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF)-alpha, and the intercellular adhesion molecule (ICAM)-1 were investigated by means of the ELISA assay. RESULTS:In the diabetic PPARgamma+/- mice, retinal leukostasis and leakage were greater than in the diabetic wild-type mice. In addition retinal leukostasis and leakage were suppressed by treatment with rosiglitazone in experimental diabetic rats. ELISA analysis revealed that the upregulated ICAM-1 expression in the diabetic rat retina was reduced by rosiglitazone treatment. CONCLUSIONS:An endogenous pathway involving PPARgamma provides protection against retinal leukostasis and retinal leakage in diabetes and treatment with PPARgamma specific ligands inhibits retinal leukostasis and retinal leakage in diabetic rats.