DIFFERENT PATTERNS OF EXPRESSION OF ORNITHINE DECARBOXYLASE MESSENGER-RNAS IN RAT-LIVER AFTER ACUTE ADMINISTRATION OF HEPATOCARCINOGENS

In the present study, we have evaluated the induction of ornithine dec arboxylase (ODC) activity in rat liver after acute in vivo administrat ion of different hepatocarcinogens, and correlated the ODC activity pe aks with the accumulation of the three ODC-related mRNA species in rat liver at different times after the intraperitoneal injection of diffe rent hepatocarcinogens. ODC activity peaked 16 h after 2-acetylaminofl uorene (2-AAF) treatment, while accumulation of the three ODC-mRNAs, s tarting 4 h after the injection, was maximal 6 h later, Thioacetamide (TAA) administration caused a single peak of ODC activity 20 h after t reatment, while there had been the maximum increases of the three ODC- mRNAs 4-h earlier, The first ODC activity peak occurred 20 h after tre atment with 3'-methyl-4-(dimethylamino)azobenzene (MDAB), at the same time that accumulation of the ODC-mRNAs was maximum, There was no incr ease in ODC-mRNA accumulation at 28 h or 36 h after MDAB treatment, th e time at which ODC activity once again peaked, All the ODC-related tr anscripts accumulated after MDAB treatment, although to different degr ees, The 1.7 kilobase (kb) transcript accumulated the most after 2-AAF treatment, After TAA treatment, the 2.2 kb mRNA was the most abundant ly expressed, In neonatal liver, in which ODC activity is physiologica lly high, the 1.7 kb mRNA is expressed more abundantly than the other two ODC-related transcripts, These results demonstrate that the peak o f ODC enzyme activity does not always correspond in time with the peak of ODC-mRNA accumulation; that different hepatocarcinogens induce dif ferent patterns of accumulation of the ODC-related transcripts; and th at the minor ODC-related transcript (1.7 kb) in rat liver seems to be expressed not only constitutively but is also inducible.