Objectives: 

The objective of this study is to investigate whether gallic acid could improve insulin sensitivity, hemodynamic alterations and oxidative stress in insulin resistant rats induced by a high fructose diet (HFD).

Materials: 

Male Sprague-Dawley rats were fed with a HFD for 14 weeks to induce insulin resistance (IR). Gallic acid, a potent antioxidant agent, (20 mg/kg) or vehicle was given further for 4 weeks with HFD feeding. Fasting blood glucose (FBG) and fasting serum insulin were performed to calculate homeostasis model assessment of insulin (HOMA-IR). Blood pressure, hindlimb blood flow (HBF), heart rate (HR) and plasma malondialdehyde (MDA) were evaluated. Data were analyzed by one-way analysis of variance (ANOVA) followed by post-hoc Duncan's multiple range tests.

Results: 

In IR rats, there were significant increases in fasting serum insulin (1.6 ± 0.3 ng/ml vs 0.3 ± 0.1 ng/ml), FBG (112.5 ± 1.7 mg/dl vs 81.7 ± 1.3 mg/dl), HOMA-IR (8.0 ± 1.2 vs 1.4 ± 0.6) comparing to those of normal control (p<0.05). Elevation of mean arterial pressure (MAP; 121.7 ± 1.7 mmHg), hindlimb vascular resistance (32.2 ± 1.4 mmHg/min/100 g/ml) and HR (386.2 ± 7.6 beat/min) were found in IR rats (p<0.05). Plasma MDA was also significantly high in IR rats (5.5 ± 0.5 mM) (p<0.05). However, IR rats received gallic acid had a significant reduction of FBG (92.9 ± 5.3 mg/dl), serum insulin (0.4 ± 0.1 ng/ml), HOMA-IR (2.2 ± 0.3), MAP (97.7 ± 1.2 mmHg), HVR (19.7 ± 1.0 mmHg/min/100 g/ml) HR (345.0 ± 8.0 beat/min) and plasma MDA (5.5 ± 0.5 mM) in IR rats compared to those of IR rats treated with vehicle (p<0.05).

Conclusions: 

This study suggests that gallic acid counteracted insulin resistance, hemodynamic alterations in IR rats. The underlying mechanism is likely to be related to its antioxidant effect.