Silymarin: potent inhibitor of cyclic AMP phosphodiesterase.

: Silymarin, the active principle of the Milk Thistle (Silybum marianum Gaertner), is a very potent inhibitor of cyclic AMP breakdown in vitro by a commercial beef heart phosphodiesterase preparation. Its main constituents, silybin, silydianin and silychristin, are 12.66 to 52.06 times more active than theophylline and 0.77 to 3.17 times more active than papaverine in this respect. Using a novel HPLC technique, the enzyme kinetical analysis can be performed much faster than by the classical methods.