Abstract: AIM: To investigate the vasorelaxant effects of total flavonoids of propoil(TFP) on isolated thoracic aorta of rats and its mechanism. METHODS: 30 male SD rats were randomly divided into four groups(n=6 each): saline control group(CG), low-, middle- and high-dose total flavonoids of propoil group(LG, MG, HG, respectively). Rats in LG, MG and HG were intragastrically (i.g) given TFP at doses with equal volume(qd), Rats in CG group were given equal volume normal saline(i.g, qd). For 4 consecutive weeks, 3-5 mL blood samples were obtained from the aorta and platelet aggregation was measured. Study was performed with the model of isolated rat thoracic aorta rings in organ bath, and the contractile reaction was observed by Phenylephrine hydrochloride injection(PE) and KCl in isolated thoracic aorta of each group.The content of Nitric oxide(NO) and the activity of inducible nitric oxide synthase(iNOS) were detected in isolated thoracic aorta of each group. RESULTS: Compared with the CG group, TFP showed a dose-dependent inhibition on the rate of platelet aggregation in rats, and a dose-dependent relaxation on the aorta rings with endothelium on the basis of pre-contracted of KCl(12-60 mmol/L); TFP improved the relaxation effect of Ach (1×10^-8-1×10^-5 mol/L) of the aorta rings on the basis of pre-contracted of PE(1×10^-6 mol/L); After pretreatment with non-selective nitric oxide synthase (NOS) inhibitor L-NAME or cyclooxygenase inhibitor indomethacin (Indo), PE(10^-8-10^-5 mol/L) induced contractile reaction of isolated thoracic aorta of TFP groups were all enhanced.Compared with the CG group, TFP showed a dose-dependent improvement with iNOS activity and NO content of thoracic aortic rings. CONCLUSION: TFP has dose-dependent inhibition on the platelet aggregation in rats and dose-dependent improvement on the relaxation of isolated rat thoracic aorta rings. Its relaxation effect is through improvement of endothelial function and the inhibition of voltage-operated calcium channels, and the function of improved endothelial function may through an increase in release of NO and prostacyclin (PGI₂). As for the mechanism of inhibition of Ca²⁺ channels, it needs further exploration.

Key words: total flavonoids of propoil(TFP), thoracic aorta rings, endothelial cell, vasodilation