Background/aim: To evaluate the effects of grape seed extract (GSE) supplementation on oxidative stress and antioxidant markers in streptozotocin (STZ)-induced diabetic rats. Materials and methods: Thirty-six male rats were divided into the following four groups: control, GSE-supplemented control, diabetic, and GSE-supplemented diabetic. Beginning on day 7 after STZ injection, the rats were administered GSE (100 mg kg -1 day -1 ) in drinking water for 6 weeks. At the end of week 6, rats were

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... rificed by cardiac puncture. Plasma nitric oxide (NO) levels and xanthine oxidase (XO), adenosine deaminase (ADA), and glutathione peroxidase (GPx) activities were analyzed. Results: Both XO and ADA activities increased and NO levels decreased in diabetic rats (P < 0.05). GSE supplementation normalized all of these changes. Antioxidant enzyme activities decreased in diabetic rats compared to the controls (P < 0.05). GSE supplementation increased antioxidant enzyme activities in both diabetic and healthy rats (P < 0.05). Conclusion: These findings suggest that 6 weeks of oral GSE supplementation may prevent oxidative stress and improve antioxidant status in diabetic rats.