Effects of tetrandrine on contractility of isolated rat uteirus

The isolated rat uterus con-traction induced by oxytocin and Ca++ after high-K+depolarization were markedly inhibited by tetrandrine (Tet). The depression was immediately reversed by addition of Ca++ to the bath fluid. Tet and verapamil (Ver), which shifted the cumulative dose-response curves to the right and depressed the maximal responses to CaCl2, acted as a non-competitive antagonist. The oxytocin-induced Cat+-dependent contractions were depressed by 4.8 and 30 uM Tet. Tet 30 uM also inhibited the Cat+-dependent component of the contraction. The effect of Ver on isolated rat uterus was stronger than that of Tet. Up to 0.05 uM, it showed no effect on Ca++-dependent oxytocin contraction. These results indicate that Tet is an effective Ca++-antagonist very similar to Ver on isolated rat uteri.