Abstract: Objective: To investigate anti-diabetic effect of grape seed polyphenols (GSP) in type Ⅱ diabetic rats, and to illustrate its underlying mechanism from the perspective of pancreatic islet damage and insulin expression. Methods: A rat model of type Ⅱ diabetes was established by injecting streptozotocin (STZ) to male SD rats. The diabetic rats were randomly divided to STZ model group, GSP treatment group (50 mg/(kg·d)), and acarbose treatment group (positive control group). GSP was administrated to diabetic rats at a dose of 50 mg/kg mb per day for 8 weeks. Serum glucose, insulin, oral glucose tolerance test (OGTT), serum superoxide dismutase (SOD) and malondialdehyde (MDA) were tested after the last administration. Islet cell damage and insulin expression were detected using immunohistochemical staining. Results: GSP decreased serum glucose level, increased OGTT, and promoted insulin secretion in diabetic rats (P < 0.05). In addition, GSP improved STZ-induced islet cell damage and increased insulin expression (P < 0.05). Serum SOD activity was increased by administration of GSP, while MDA content was decreased significantly (P < 0.05). Conclusion: A long-term intervention with low-dose GSP can effectively regulate blood glucose in diabetic rats. GSP promotes insulin secretion by rescuing islet cell damage, thereby decreasing fasting serum glucose level and increasing OGTT, which may be associated with its potent antioxidant activity in vivo.

Key words: grape seed polyphenols, hypoglycemia, insulin, islet cell damage