Increased RNA synthesis in nuclei isolated from rat liver tissue slices incubated with cyclic adenosine 3′,5′-monophosphate or glucagon

Abstract

Incubation of rat liver tissue slices with cyclic adenosine 3′,5′-monophosphate (cyclic AMP) for 30 min results in a dose-dependent increase in RNA synthesizing capacity of nuclei prepared from these slices, with a doubling of synthetic rate observed at 10 −7 m cyclic AMP. The cyclic AMP effect is observed when RNA polymerase activity is measured either in the presence of Mg 2+ and low ionic strength, or Mn 2+ and high ionic strength. Experiments employing saturating amounts of exogenous bacterial RNA polymerase suggest that the cyclic AMP-induced stimulation occurs primarily at the level of template activity. Other cyclic nucleotides tested in the same manner are ineffective in stimulating RNA synthesis by tissue slice nuclei. In addition to cyclic AMP, adenosine 5′-monophosphate (5′-AMP) consistently produced small increases in nuclear RNA synthesis although never of the magnitude seen with the cyclic nucleotide. An increased capacity for RNA synthesis is also seen in nuclei isolated from liver slices incubated with glucagon at concentrations from 0.5 μg/ml to 50 μg/ml. A maximal stimulation of approximately twofold occurs at a glucagon concentration of 1.0 μg/ml. Liver slices incubated with optimal concentrations of cyclic AMP and glucagon simultaneously show that the effects of the two agents on RNA synthesis are not additive. The results indicate that cyclic AMP at physiological concentrations can stimulate RNA synthetic capacity in vitro, and that the effect mimics a similar response to glucagon. Since it is known that glucagon causes an increase in liver concentrations of cyclic AMP and a subsequent induction of some liver enzymes, it is suggested that cyclic AMP-mediated control of RNA synthesis may be involved in such regulation.