Effects of glycyrrhizin on thymolytic and immunosuppressive action of cortisone.

Glycyrrhizin has been clinically used as an anti-allergic agent, but its mechanism remains unknown. This study was undertaken to examine the effect of glycyrrhizin on thymolytic and immunosuppressive action of cortisone in normal rabbits and adrenalectomized rats. Immunization was performed by injection of bacterial a-amylase emulsified in Freund's incomplete adjuvant. Antibody titer of the serum was expressed as the enzyme-neutralizing activity. The circulating antibody could be detected in normal rabbits about 10 days after immunization and elevated lineally thereafter. The antibody titer was suppressed to one half and to one fourth of the control by administration of 15mg/Kg and 30mg/Kg of glycyrrhizin respectively. Glycyrrhizin had no effect on the antibody titer in the case of adrenalectomized rats, though the titer of the control in these rats was lower than that in normal rabbits. Cortisone treatment resulted in the decrease of the titer. By concomitant administration of glycyrrhizin with cortisone the antibody titer was much more decreased, thus showing an enhancing effect of glycyrrhizin on immunosuppressive action of cortisone. On the other hand, thymolytic action of cortisone was inhibited by concomitant administration of glycyrrhizin on the basis of thymus weight in rats. This effect of cortisone was blocked by glycyrrhizin. Glycyrrhizin by itself had no significant effect on thymus weight. The dissociation of the effect of glycyrrhizin on these cortisone actions suggests that one biological action of cortisone might come through some different mechanism from another. Mechanisms of the action of glycyrrhizin were discussed in relation to various biological actions of cortisone.