Mechanism of the stimulation of RNA synthesis in rat liver nuclei by silybin.

The influence of the flavonolignane derivatives silybin, silybinhemisuccinate and silybindihemisuccinate on the RNA synthesis in isolated nuclei from rat livers was studied. A stimulatory effect of silybin on the incorporation of [3H]UTP into nuclear RNA was found and the dose dependence could be demonstrated. The results support former findings that silybin stimulates RNA synthesis in rat livers in vivo and in hepatocytes. Experiments with purified nucleoli indicated that mainly the rate of rRNA synthesis is increased. The mechanism of this stimulation was elucidated by experiments with isolated RNA polymerases. It could be demonstrated that polymerase B is not affected by the flavonolignane, but the activity of polymerase A is increased, due to higher V at constant Km values. Thus silybin is shown to be an enzyme-stimulating effector.