Mechanisms for the vasodilations induced by Ginkgo biloba extract and its main constituent, bilobalide, in rat aorta

Vasodilating actions of Ginkgo biloba extract (GBE) and bilobalide, a main constituent, were examined using rat aorta ring strips. GBE at the concentration ranges from 0.03 to 3 mg/ml had a potent concentration-dependent relaxation, reaching 70 +/- 4.5% (n = 6, P < 0.001) at 3 mg/ml. Bilobalide at 0.1 to 100 mu M also caused the relaxation in a concentration-dependent manner. At 100 mu M, bilobalide caused dilation by 17.6 +/- 3.9% (n = 7, P < 0.05). NG-monomethyl-L-arginine acetate (L-NMMA)(100 muM), an NO synthesis inhibitor, reduced the vasodilation of GBE (3 mg/ml) to 57.6 +/- 2.5% (n = 6, P < 0.05), and was accompanied with a decrease in the rate of relaxation. Tetraethylammonium (TEA)(100 mu M), a Ca2+-activated K+ channel inhibitor, also decreased the GBE (3 mg/ml)-induced relaxation to 63.1 +/- 4.6% (n = 6), but not significantly. Indomethacin tended to reduce the GBE (3 mg/ml)-induced vasorelaxation to 67.3 +/- 4.1% (n = 6). In contrast, the vasorelaxation of GBE (3 mg/ml) was strongly attenuated to 53 +/- 6.1% (n = 7, P < 0.05) in Ca2+-free medium. Similarly, the vasorelaxation induced by bilobalide significantly decreased both by pretreatment with NO inhibitor (L-NMMA) and in Ca2+-free solution. These results indicate that the relaxation induced by GBE would be due to the inhibition of Ca2+ influx through the Ca2+ channel and the activation of NO release, and might be in part due to the inhibitions of Ca2+-activated K+ current and PGI(2) release, in the endothelium and aortic vascular muscles. Bilobalide possesses the similar mechanisms for the vasodilation. (C) 2003 Elsevier Science Inc. All rights reserved.