Endothelium-independent relaxation of aorta rings by two stilbenoids from the orchids Scaphyglottis livida.

Gigantol (1) and 3,7-dihydroxy-2,4-dimethoxyphenanthrene (2) from the orchid Scaphyglottis livida induced a significant concentration-dependent relaxation of the contractions evoked by noradrenaline (NA) in endothelium-intact and denuded rat aorta rings. Incubation with N(G)-nitro-L-arginine methyl ester (L-NAME, 1x10(-5) M) or methylene blue (MB, 1x10(-7) M) significantly reduced the relaxation induced by the stilbenoids 1 and 2. The results suggested that two or more mechanisms are involved in the vasorelaxant effects of both compounds.