Some effects of aflatoxin B 1 on RNA synthesis in rat and mouse liver

Abstract

Rat liver Mn 2+ and Mg 2+ activated RNA polymerase activities, assayed in vitro are inhibited by aflatoxin B 1 administered in vivo, whereas the enzyme activities in mouse liver are not. [ 14C]orotic acid incorporation in vivo into rat liver RNA is inhibited by aflatoxin B 1 administered in vivo, whereas incorporation into mouse liver RNA is not. Mg 2+ activated RNA polymerase and [ 14C]orotic acid incorporated into RNA in both rat and mouse liver are inhibited by incubating liver slices in vitro in the presence of aflatoxin B 1. No significant inhibition of hepatic Mg 2+ activated RNA polymerase by aflatoxin B 1, administered in vivo, is observed when rats are pre-treated with phenobarbitone. These data demonstrate that RNA synthesis in mouse liver is potentially capable of being inhibited by aflatoxin B 1 and suggest that the level of microsomal metabolism is an important factor in determining the presence or absence of inhibition. Attempts, using SKF 525 A treated mice, to demonstrate inhibition by aflatoxin B 1 in vivo of mouse liver RNA polymerase were unsuccessful. Incubation studies in vitro however, indicated that SKF 525 A did not significantly affect the overall rate of metabolism of aflatoxin B 1 by liver slices or microsomal preparations.