Glycyrrhizin (GLR) and its newly synthesized derivatives, deoxoglycyrrhetol dihemisuccinate (I), deoxoglycyrrhetol dihemiphthalate (II), and the related compounds, carbenoxolone and glycyrrhetinic acid hemiphthalate (III), were assayed with or without paeoniflorin (PF) in mice diaphragm muscles. GLR-derivatives per se blocked the nerve-stimulated twitch tensions with the following order of potencies: carbenoxolone=III>II=I>GLR. The potencies paralleled the extent of muscle depolarization except in the case of I. GLR and I only increased muscle conductance. The blocking effects by GLR-derivat!ves per se on twitch responses are, therefore, can be explained by depolarization of muscle membranes and not by membrane conductance change. When carbenoxolone, II or GLR were blended with PF, the potentiation of the blocking effects observed may be related to the muscle depolarization rather than by the increase in membrane conductance.
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