Subchronic administration of caffeine and theophylline in drinking water: effects on rat liver RNA polymerase I activity.

Administration of caffeine or theophylline, 0.2 mg/ml (an average of 20 mg/kg/d) of drinking water, to male CD rats, 2 months of age, over a 15 week period resulted in the elevation of liver RNA polymerase I activity by 2-3 fold as assayed in isolated nuclei. This increase in activity was already apparent by the fourth week of exposure. The changes in RNA polymerase I activity were accompanied by moderate liver hypertrophy.