Effects of hawthorn leaf flavonoids on contraction and relaxation in isolated rat thoracic aortic rings

Objective To investigate the effects and mechanisms of hawthorn leaf flavonoids (HLF) on isolated thoracic aorta in rats. Methods The tension of rat thoracic aorta tings was measured.The effects of HLF on the thoracic aorta preconstricted by potassium chloride ( KCl, 6 × 10-2 mol/L) and norepinephrine (NE, 1 × 10-6 mol/L), as well as the effects of L-nitro arginine methyl ester (L-NAME,1 × 10-5 mol/L) and indomethacin ( 1 × 10-4 mol/L) on the relaxation response of HLF were observed.Results HLF completely relaxed the constriction induced by NE ( 1 × 10 -6 mol/L) in endothelium-intact thoracic aorta ( P ＜ 0. 01 ), but had no effect on those preconstricted aorta rings by a high concentration of KCl (6 × 10-2 mol/L) in endothelium-intact and endothelium-denuded rat aorta (P ＞ 0. 05). The relaxation response of HLF was significantly inhibited by L-NAME (P ＜ 0. 01 ), but not by indomethacin (P ＞0. 05). Conclusion The vasorelaxation induced by HLF in rat aorta rings may involve the reduction of Ca2+ influx through the calcium channels operated by receptor (ROC). The endothelium-dependent relaxation of HLF may be related to the generation of nitric oxide (NO). Key words: Hawthorn leaf flavonoids;  Thoracic aorta rings;  NO