Mechanism of the Stimulation of RNA Synthesis in Rat Liver Nuclei by Silybin

Abstract

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. Former findings are supported 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 [EC2.7.7.6]. Polymerase B appears not to be affected by the flavonolignane, but the activity of polymerase A is probably increased due to higher V [velocity] at constant Km values. Thus silybin is apparently an enzyme-stimulating effector.