Oxidative stress is one possible pathogenic mechanism to explain diabetic microangiopathy. In the present study, we determined the antioxidant enzyme activities in bovine retinal microvessels and cultured retinal microvascular cells: endothelial cells (BREC) and pericytes (BRP). We further investigated the effects of high glucose and advanced glycation end products (AGE) on these enzyme activities in BREC and BRP. Antioxidant enzyme activities in native retinal microvessels and BREC were quite similar but differed markedly from the BRP ones. High glucose decreased Se-GPx activity (about 20%) in BREC compared to mannitol. High concentrations of mannitol or NaCl increased Se-GPx activity (up to 40%) compared to control medium, suggesting that hyperosmolarity could regulate Se-GPx in BREC. No changes in antioxidant enzyme activities were observed when BRP were cultured with glucose or mannitol at high concentrations. AGE-BSA had no effect on enzyme activities in BREC, whereas 20 microM AGE-BSA increased catalase (40%) and superoxide dismutase (60%) activities in BRP. Differences in antioxidant enzyme activities observed between BREC and BRP, cultured with high concentrations of glucose or AGE, might help to explain their different behavior during the pathogenesis of diabetic retinopathy, i.e., early pericyte drop-out and late endothelial cell proliferation.