Pressor mechanism of tussilagone

Tussilagone (14R, 7R)-14-acetoxy-7-[(2’E)-3’-methylpent-2’-enoyloxy]-oplopanone, first isolated by Chinese from Tussilago farfara L, had a prominent pressor effect on spinal cats and a slight depressor effect on anesthetized cats injected via vertebral artery. The pressor effect was not influenced by hexamethonium bormide, but reduced by phentolamine or premedication of reserpine. Tussilagone induced the contraction of aortic strips of rabbits. The contractile pattern was not influenced by phentolamine or verapamil, but reduced in Ca2+-free solusion. This was different from that of norepinephrine.
These results indicate that the vasoconstricting effect of tussilagone is peripheral, and is a combined results of increasing the release of catecholmince transmitter from nerve terminals and a direct action on vascular smooth muscle. The direct action depends on the extracellular Ca2+.