Nitric oxide and endothelium-dependent effect of Tribulus terrestris feeding on aortic reactivity of streptozotocin-diabetic rats

Background and Objective: Cardiovascular disorders continue to constitute major causes of morbidity and mortality in diabetic patients. In this study, the effect of chronic administration of Tribulus terrestris (TT) feeding was studied on aortic reactivity of streptozotocin (STZ)-diabetic rats and some underlying mechanisms were investigated.    Materials and Methods: Male diabetic rats received TT-mixed food at a weight ratio of 6% for 7 weeks 1 week after diabetes induction. Contractile responses to KCl and phenylephrine (PE) and relaxation response to acetylcholine (ACh) were obtained from aortic rings in the presence and absence of endothelium. In addition, nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) was used to determine the role of NO. Results: Maximum contractile response of endothelium-intact rings to PE was significantly lower in TT-treated diabetic rats relative to untreated diabetics and endothelium removal abolished this difference. Endothelium-dependent relaxation to ACh was also significantly higher in TT-treated diabetic rats as compared to diabetic ones and pretreatment of rings with L-NAME significantly attenuated the observed response. Conclusion: Chronic treatment of diabetic rats with TT could prevent some abnormal changes in vascular reactivity in diabetic rats through nitric oxide in aortic tissue and endothelium integrity is necessary for this beneficial effect.