Possible mechanism of steroid action of the plant herb extracts glycyrrhizin, glycyrrhetinic acid, and paeoniflorin: inhibition by plant herb extracts of steroid protein binding in the rabbit.

To assess the action of some components of herbal medicine, glycyrrhizin, glycyrrhetinic acid, and paeoniflorin, on steroids, their binding to several classes of intracellular and serum steroid-binding proteins were studied in the rabbit. The affinity (inhibitor constant) for binding of dihydrotestosterone-sex hormone binding globulin in the serum (dissociation constant of 2.0 nmol/L for dihydrotestosterone) was approximately 520 nmol/L, and that for the binding of cortisol-corticosteroid-binding globulin in the serum (dissociation constant of 2.0 nmol/L for cortisol) was approximately 10 mumol/L. In the uterine cytosol, the inhibitor constant value for estradiol receptor binding (dissociation constant of 1.0 nmol/L) was 0.9 mumol/L, and these compounds did not influence progestin receptor binding (dissociation constant of 1.4 nmol/L). The inhibitor constant values for glucocorticoid receptor binding (dissociation constant of 1.0 nmol/L) in the liver cytosol were 3.0 nmol/L for paeoniflorin, 2.0 nmol/L for glycyrrhizin, and 1.7 nmol/L for glycyrrhetinic acid, and those for mineralocorticoid receptor binding (dissociation constant = 1.1 nmol/L) in the kidney cytosol were 3.5 nmol/L for paeoniflorin and glycyrrhetinic acid and 3.0 nmol/L for glycyrrhizin. These results suggest that herbal extracts such as the above compounds influence steroid effects by glucocorticoid and mineralocorticoid receptors and to a lesser extent by estrogen receptors or serum sex hormone-binding globulin and corticosteroid-binding globulin.