The vasodilatory and antioxidant activities of polyphenolic substances
This project was designed to determine the effect of a wide range of grape and tea based extracts and green tea catechins on vascular tension in vitro, further determine the relationship between their vasodilatory and antioxidant activities and identify the major polyphenols present in green and black tea. Grape and tea based extracts were examined for their vasodilator activity in vitro using standard organ bath pharmacology. All extracts evoked biphasic concentration-dependent relaxation in rabbit aortic vessels. Grape based extracts were significantly better vasodilators than tea based extracts. Previous work by others has shown that grape based products induce vascular relaxation via nitric oxide (NO) and endothelium-dependent mechanisms. This study demonstrated that a range of grape based extracts induced vasorelaxation responses via complex mechanisms including endothelium-dependent and independent mechanisms via vasodilating prostaglandins by way of prostacyclin and endothelial NO production. Tea based extracts on the other hand, induced vasorelaxation via the combined interactions of vasodilating endothelium-dependent prostaglandins. The relationship between the vasodilation capacity, antioxidant activity, based on the reduction of the free Fremy's radical and ferric reducing power, and total phenolic content of each extract was also determined. In general, a significant inverse correlation was identified between the vasodilator abilities of the grape and tea extracts in vitro and their antioxidants activities. This study demonstrates that grape and tea based extracts induce vasorelaxation in isolated rabbit aortic vessels and are effective antioxidants in vitro, within a concentration range that may be reached in vivo by moderate wine and tea consumption. The results presented here also indicate that consumption of green tea may have greater benefits than consumption of black tea in terms of their vasodilatory activity and antioxidant capacity in vitro.