Vascular activity of protopanaxadiol and protopanaxatriol, the major saponin fractions isolated from roots of Panax notoginseng

Background: Panax notoginseng (PN) (Burk) F. H. Chen (Araliacea) is a Chinese herb commonly known in Asia for its medicinal potentials, antihypertensive included. The aim of this study was to investigate the vasorelaxant activity of protopanaxadiol (PDS) and protopanaxatriol (PTS), the major saponin fractions isolated from roots of PN, and identify the underlying mechanisms on isolated rat aortic rings. Methods: Radnoti Tissue-Organ bath instrument (ADInstruments) was used to perform Tissue-Organ bath experiments, and tensions produced on isolated rat aortic rings were recorded by the help of ADInstruments PowerLab 8/30 system (Model ML 870, Australia). Results: Both PDS and PTS (10-6-10-3 μg/ml) induced concentration-dependent relaxations in intact rat aortic rings pre-contracted with norepinephrine (1 μM).This activity was considerably reduced after removal of the endothelium and in intact rings pre-treated with NG-nitro-L-arginine methyl ester (L-NAME, 100 μM), 1H-[1,2,4]-oxadiazole-[4,3-α]-quinoxaline-1-one (ODQ, 10 μM), and combination of L-NAME and ODQ. However, pre-treatment with indomethacin (10 μM) did not affect either PDS- or PTS-induced relaxations. Furthermore, both PDS and PTS (10-4 and 10-3 μg/ml) decreased CaCl2- and potassium chloride (KCL)-induced vasoconstrictions in a dose-dependent manner. Our findings suggest that both PDS and PTS produced vasorelaxant effect that was mediated by NO-cyclic guanosine monophosphate in intact rings and by blockade of calcium influx in vascular smooth muscle. Cyclooxygenase pathway, on the other hand, had no apparent role. Among these fractions, PDS showed better effect with a slight difference. Conclusion: Findings from this study showed that both PDS and PTS fractions possess vasorelaxant activity. This supports the potential use of PN in management of cardiovascular diseases, especially hypertension.