INOTROPIC EFFECTS OF TANGHININ AND ACETYL-TANGHININ ON GUINEA-PIG ISOLATED PAPILLARY-MUSCLE

Tanghinin and its acetylated derivative acetyl-tanghinin are two cardiotonic glycosides isolated from the seed of Tanghinia venenifera Poir. (Apocynaceae). In vitro, these two heterosides increase the contractile force of the guinea-pig papillary muscle. At an extracellular concentration of 1.2 mM of CaCl2, a concentration of 2.8 x 10(-6) M of tanghinin or acetyl-tanghinin increased muscle tension with 1.3 g and 1.5 g, respectively. In presence of an extracellular concentration of 2.4 mM of CaCl2, maximal effects-1.8 g for tanghinin and 2.2 g for acetyl-tanghinin-were obtained with a glycoside concentration of 2.4 x 10(-6) M. These maximal effects are sustained up to a concentration of 2.8 x 10(-6) M. At higher concentrations, the positive inotropic effect drops rapidly, followed by a rise in diastolic tension.