Effects of tetrandrine on release of calcium-dependent endothelium-derived relaxant factor

In calcium-free Krebs solution, the inhibition of endothelium-dependent relaxation induced by acetylcholine (ACh) in rabbit aortic rings was observed, but the inhibition was antagonized when Ca2+ was added. In KCl 40 mmol/L and phenylephrine (PE) 1 μmol/L groups, the relaxations evoked by ACh in aortic rings were not inhibited by tetrandrine (Tet)<30 μmol/L and verapamil (Ver)<10 μmol/L, but were suppressed by Tet 30 μmol/L and Ver 10 μmol/L. It is concluded that the release of endothelium-derived relaxant factor (EDRF) induced by ACh is depended on extracellular calcium. The stimulated liberation of EDRF is inhibited by a large dose of Tet (30 μmol/L) or Ver (10 μmol/L). The results may indicate that the characteristics of calcium channel of endothelial cells are not identical with those of the smooth muscle cells.