Abstract: To study the effect of total flavonoids of Ampelopsis megalophylla, dihydromyricetin and myricetin on thoracic aorta rings of rats,a biological signal collection and analytical system was applied to observe the tension of resting thoracic aorta rings and the doseeffect curve of the contractile response induced by noradrenaline (NA).The results showed that A.megalophylla flavonoids,dihydromyricetin and myricetin can increase the tension of resting thoracic aorta rings in a dosedependent manner.The total flavonoids of A.megalophylla shifted the dose-effect curve of the contractile response induced by NA to the right and decreased their maximal efficiency (E_max).The similar effects were also observed in dihydromyricetin and the mixture of dihydromyricetin and myricetin,wherein the mixture lowered much more E_max than either of the two isolets applied individually.In particular,the mixture comprising of dihydromyricetin and myricetin with concentration ratio of 10:1 showed better effect.In conclusion,flavonoids of A.megalophylla induced dose-dependent contraction in isolated thoracic aorta rings in rats and can significantly noncompetitively antagonize NA induced contraction of rat aortic rings.In addition,dihydromyricetin and myricetin synergistically antagonize NA induced contraction of vascular rings with optimal ratio of 10:1.

Key words: flavonoids of Ampelopsis megalophylla, dihydromyricetin, myricetin, thoracic aorta rings