Vasorelaxant effect of the rootbark extract of Paeonia moutan on isolated rat thoracic aorta

The vascular relaxant effect of the rootbark extract of Paeonia moutan was evaluated in isolated rat thoracic aorta. The methanolic extract of the rootbark showed a vasorelaxant activity in rat aortic preparations precontracted with 0.3 microM phenylephrine (IC50 value: 16.8 microg/mL). The activity-guided fractionation of the extract led to the isolation of five active principles such as paeoniflorin (1), paeonidanin (2), methylpaeoniflorin (4), tetragalloylglucose (5) and pentagalloylglucose (6), and these active ingredients potently relaxed phenylephrine-induced contraction of rat aortic preparations in a concentration-dependent manner (IC50 values: 19.4, 7.9, 10.1, 5.1 and 3.6 microM, respectively). These results suggest that pinane glycosides and galloylglucoses might be the components responsible for the vasorelaxant properties of the rootbark extract of P. moutan, and their vasorelaxant effects may be mediated through increases in the release of nitric oxide from endothelial cells.