Soybean feeding improves vascular dysfunction and atten-uates oxidative stress in streptozotocin-diabetic rats

Background and Objective: The effect of chronic dietary soybean (Glycine max L.) on aortic reactivity of streptozotocin (STZ)-diabetic rats was studied. Materials and Methods: Male diabetic rats received soybean for 7 weeks 1 week after diabetes induction at weight ratios of 3 and 6%. Contractile responses to KCl and phenylephrine (PE) and relaxation response to acetylcholine (ACh) were obtained from aortic rings. Results: Maximum contractile response of endothelium-intact rings to PE was significantly lower in soybean6%-treated diabetic rats relative to untreated dia-betics (p < 0.05) and endothelium removal abolished this difference. Endotheli-um-dependent relaxation to ACh was significantly higher in soybean6%-treated diabetic rats as compared to diabetic ones (p < 0.05) and pretreatment of rings with nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) and/or indomethacin attenuated it. Two-month diabetes also resulted in an elevation of malondialdehyde (MDA) and decreased superoxide dismutase (SOD) activity and soybean treatment significantly reversed the increased MDA content and reduced activity of SOD. Conclusion: Therefore, chronic treatment of diabetic rats with soybean could dose-dependently prevent some abnormal changes in vascular reactivity in dia-betic rats through nitric oxide- and prostaglandin-related pathways and via attenuation of oxidative stress in aortic tissue and endothelium integrity seems essential for this effect.