Endothelium-dependent and-independent effects of Vaccinium myrtillus feeding on contractile reactivity of thoracic aorta from diabetic rats

Diabetes mellitus is followed by higher incidence of cardiovascular disorders. There is some evidence on protective and antidiabetic effects of Vaccinium myrtillus (VM). Thus, the endothelium-dependent and –independent effect of oral administration of VM for 6 weeks on contractile and relaxatory response of thoracic aorta from diabetic rats was investigated. Male rats were divided into control, VM-treated control, diabetic and VM-treated diabetic groups. Treated groups received VM-mixed pelleted food at a weight ratio of 5%. Body weight and serum glucose levels were measured before the study and at weeks 3 and 6. At the end of study, contractile reactivity of thoracic aortic rings to KCl and phenylephrine and relaxatory response to acetylcholine (with endothelium) and sodium nitroprusside (without endothelium) was determined using isolated tissue setup. Serum glucose levels significantly decreased in VM-treated diabetic group versus untreated diabetics (p=0.04). In addition, endothelium-intact VM-treated diabetic group showed a significantly lower contraction to KCl and phenylephrine (p=0.04) as compared to diabetic group and endothelium removal reduced this difference. Meanwhile, relaxation response of endothelium-intact rings to acetylcholine was significantly higher in VM-treated diabetic group as compared to diabetics (p=0.02). Chronic oral administration of VM through affecting synthesis and release of endothelial vasoactive agents and also via direct effects on vascular smooth muscle could decrease contractile and enhance relaxatory responses in aortic tissue of diabetic rat. These effects may have the beneficial effects in prevention of some long-term vascular complications of diabetes.