On Relationships between Induction of Liver Cancer with Azo Dyes and Changes in Nuclear RNA Metabolism During Carcinogenesis

Summary

The purpose was to determine whether changes in hepatic nuclear RNA synthesis and content were correlated with tumor incidence in rats fed 4′-F-DAB or 3′-Me-DAB. Rats were fed 4′-F-DAB for 6 weeks in diets that potentiated (“Medes'diet”) or retarded (“Farber's diet”) hepatic cancer induction. Other rats were fed 3′-Me-DAB in “Medes'diet” or “Farber's diet,” but, risks for hepatic cancer induction were essentially identical. RNA synthesis was adjudged by incorporation of orotic acid-6-¹⁴C or adenine-8-¹⁴C into 2 nuclear RNA subfractions obtained by neutral salt extraction. Results were: (a) incorporation of labeled orotic acid into nucleolar RNA was inhibited by both azo dyes in correlation with expected tumor incidence, incorporation into non-nucleolar nuclear (NNN) RNA was inhibited by 3′-Me-DAB in one diet, but not by 4′-F-DAB; (b) incorporation of labeled adenine into NNN RNA was stimulated by both azo dyes but not in correlation with expected tumor incidence, incorporation into nucleolar RNA was not changed; and (c) RNA content of both fractions was not appreciably changed. It was concluded that no consistent relationship appeared to exist between liver tumor induction with these 2 azo dyes and changes in these aspects of nuclear RNA metabolism during carcinogenesis.