Relation between induction of rat hepatic ornithine decarboxylase activity by tumor promoters 12-O-tetradecanoylphorbol-13-acetate and phenobarbital and levels of the polyamines putrescine, spermidine and spermine, in vivo; differential effects of retinyl-acetate

A single i.p. injection of 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a transient increase in the levels of rat liver putrescine, spermidine and spermine. These polyamine concentrations continuously increased until 6 h, immediately following administration of the tumor promoter. Phenobarbital (PB) induced an increase of the putrescine and spermidine concentrations during the 8 h post administration studied, while spermine reached a plateau after 4 h. When retinyl-acetate (RA) was injected one hour prior to TPA, the increases of the polyamines were considerably inhibited. This treatment with RA partially inhibited further increase of putrescine and spermine by PB. These findings are discussed in respect to the concomitant ornithine decarboxylase (ODC) activities, we have previously reported. I.p. injection of RA alone caused an elevation of ODC activity as well as putrescine and spermidine concentration within 2 h of exposure.