INFLUENCE OF THE ABSOLUTE-CONFIGURATION ON THE VASCULAR EFFECTS OF TETRANDRINE AND ISOTETRANDRINE IN RAT AORTA

The relaxant action of (1S, 1'S) tetrandrine and its isomer (1R, 1'S) isotetrandrine were examined in rat aortic strips, in presence or abse nce of extracellular calcium. Both alkaloids relax, concentration depe ndently, the contractile response elicited by depolarizing solution (K Cl 80 mM) or noradrenaline (1 mu M). Tetrandrine, however, showed a se lectivity of action towards the KCl-induced contraction while isotetra ndrine did not. In Ca2+-free solution, both alkaloids inhibited the co ntraction induced by noradrenaline, but they did not affect the transi ent contraction due to caffeine then this effect is not attributable t o direct inhibition of the smooth muscle contractile elements. The ref illing of intracellular calcium stores sensitive to noradrenaline or c affeine was significantly inhibited by both alkaloids.