Effects of tetrandrine on inotropic and toxic actions of cardiac glycosides and its relation to extracellular calcium
Chen, Y.Y.; Fang, D.C.; Lü, F.H.
Zhongguo Yao Li Xue Bao 3(3): 175-178
1982
ISSN/ISBN: 0253-9756 PMID: 6216726 Document Number: 190452
The effects of tetrandrine (T) or Ca2+ on inotropic and toxic actions of 2 cardiac glycoside preparations, divasid and ouabain, were studied in isolated leaf atria of rabbits. Divasid was extracted from Strophanthus divaricatus, with divaricoside as the main constituent. The inotropic and toxic effects of ouabain were enhanced as the concentration of extracellular Ca2+ was increased. Divasid differs from ouabain. With 0.9-2.4 mM Ca2+, the time of peak effect (PET) and toxic effect (TET) of divasid did not differ significantly. The dependence of ouabain on extracellular Ca2+ was more marked than that of divasid. Tetrandrine at a low but still hypotensive effective concentration (4.8 .mu.M) prolonged PET and reduced the toxicity of the 2 preparations. No effect on the degree of contraction amplitude increment was observed. These effects of tetrandrine are not attributable to its negative inotropic action. Since they were antagonized by Ca2+, it may be assumed that tetrandrine is a Ca antagonist.