Effects of dietary feeding of aflatoxin B1 on ribosomal RNA metabolism in rat liver

S. J. Smith, K. C. Deen, W. J. Calhoun, H. F. Beittenmiller

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After 1 wk of dietary feeding of aflatoxin B1 (AFB1) (1 or 10 ppm) to male Fischer rats, sucrose gradient analysis revealed decreases in the incorporation of [3H]orotic acid in vivo into 45 S hepatic nRNA when compared with controls fed an identical diet minus AFB1. Sucrose gradient analysis of hepatic microsomal rRNA showed decreases of a similar magnitude in labeling in vivo and in A260 of 28 S rRNA. Labeling and A260 of the 18 S rRNA were unchanged. Assay of RNA polymerase I activity in isolated hepatic nuclei demonstrated that this enzyme activity was not diminished in rats fed the AFB1 diet from that of the controls. Feeding of AFB1 for 1 to 6 wk resulted in progressive decreases in A260 of 28 S nRNA and in both label and A260 in microsomal 28 S rRNA. These effects are time and dose related, since 1 wk of a diet containing 10 ppm produced changes in nuclear and ribosomal 28 S RNA similar to those observed after 4 to 6 wk of a diet containing 1 ppm. Sixteen hr after a single injection of AFB1 (1 mg/kg i.p.), the same defects in RNA metabolism occurred as described above for 1 ppm for 4 to 6 wk and 10 ppm for 1 wk. In contrast to the chronic feeding studies, after an acute injection these effects eventually disappear. These data suggest that early progressive lesions in the maturation of hepatic 28 S rRNA are produced during chronic feeding of a diet containing AFB1. Such defects in processing of ribosomal precursor RNA may be a characteristic feature of chemical hepatocarcinogenesis.

Original languageEnglish (US)
Pages (from-to)I
JournalCancer Research
Issue number7
StatePublished - 1977
Externally publishedYes

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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