Transcriptional and translational control of nafenopin-induced ornithine decarboxylase activity in rat liver.

The induction of liver ornithine decarboxylase activity by nafenopin was studied in rats. The alpha-adrenergic antagonist, phentolamine, injected 0.5 hr before nafenopin, greatly potentiated the response. Actinomycin D, injected before nafenopin, did not affect nafenopin-induced ornithine decarboxylase activity whereas the potentiating effect of phentolamine was inhibited. In contrast, administration of actinomycin D 5.0 hr after nafenopin markedly enhanced nafenopin-induced activity. The induction of ornithine decarboxylase activity by nafenopin, as well as the potentiating effect of phentolamine was inhibited by 1,3-diaminopropane and cycloheximide, implying a requirement for synthesis of new enzyme protein for both effects. These results suggest that nafenopin induced ODC through a posttranscriptional mechanism whereas the potentiating effect of phentolamine requires transcription of new messenger RNA.