Stimulation of ornithine decarboxylase and nuclear RNA polymerase activity in rat liver by glucagon and dibutyryl cyclic amp.

Abstract

ABSTRACT The influence of glucagon and dibutyryl cyclic 3′,5′-AMP on ornithine decarboxylase (EC 4.1.1.17) and nuclear RNA polymerase (EC 2.7.7.6) activity of rat liver was studied. Intraperitoneal administration of 0.2 mg of glucagon per 100 g body weight resulted in a four- to six-fold increase in ornithine decarboxylase activity. This enzyme activity was also markedly increased by a single ip injection containing 2.5–5 mg of dibutyryl cyclic AMP. The time course of this effect demonstrated a maximum at 3–4 h. Both agents also stimulated nuclear RNA polymerase activity. The increase in hepatic ornithine decarboxylase activity by dibutyryl cyclic AMP was not abolished by adrenalectomy but was totally prevented by the administration of actinomycin D, α-amanitin and cycloheximide, which suggests that the increase in activity represents synthesis de novo of the enzyme. A sharp rise in liver ornithine decarboxylase activity was also observed after administration of theophylline, whereas no change in enzyme activity was found after the administration of adenosine or adenosine 5′-nucleotides.