Effect of polycyclic aromatic compounds and phorbol esters on ornithine decarboxylase and aryl hydrocarbon hydroxylase activities in mouse liver.

Single i.p. injections of 3-methylcholanthrene (MC; 50 mg/kg) administered to inbred C57BL/6 mice or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 100 micrograms/kg) to DBA/2 mice gave an increase in the hepatic activities of ornithine decarboxylase (ODC) and aryl hydrocarbon hydroxylase (AHH) with peaks occurring by 12 and 48 hr, respectively. A single i.p. dose of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA; 100 micrograms/kg) enhanced the activity of ODC about 70-fold within 12 hr in C57BL/6 mice and 18-fold within 24 hr in DBA/2 mice without affecting AHH activity markedly. 4-O-Methyl-12-O-tetradecanoylphorbol-13-acetate (100 micrograms/kg) raised ODC activity to about 25% of the TPA-treated value in C57BL/6 mice; in DBA/2 mice, TPA and 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate induced ODC activity to roughly the same level. Benzo(e)pyrene (50 mg/kg) failed to affect ODC and AHH activities significantly in either strain. The inducing effect of TPA on ODC activity was potentiated by a simultaneous administration of MC to C57BL/6 mice; combined TPA and TCDD to DBA/2 mice exerted an additive effect on hepatic ODC activity. Difluoromethylornithine administered i.p. effectively inhibited the induction of ODC activity elicited by TPA, MC, or TCDD either alone or in various combinations but did not interfere with AHH induction. These data indicate that different regulatory factors are involved in the ODC induction process elicited by TPA and polycyclic aromatic compounds and that MC and TCDD may induce ODC activity by different mechanisms. The results also confirm our earlier findings in rat skin and cells in culture which suggest that the ODC and AHH induction processes can occur independently of each other. Additionally, there is a strain-related difference in sensitivity with regard to ODC-inducing activity of TPA in the livers of C57BL/6 and DBA/2 mice.