Inhibition by indomethacin and 5,8,11,14-eicosatetraynoic acid of the induction of rat hepatic ornithine decarboxylase by the tumor promoters phenobarbital and 12-O-tetradecanoylphorbol-13-acetate in vivo.

The involvement of arachidonate metabolism in the induction of rat hepatic ornithine decarboxylase (ODC) activity by the tumor promoters 12-O-tetradecanoylphorbol-13-acetate (TPA) and phenobarbital (PB) was investigated. Pretreatment of the rats with indomethacin or 5,8,11,14-eicosatetraynoic acid dose dependently inhibited the induction of ODC by both tumor promoters. Both inhibitors were more potent inhibitors of PB induction than TPA induction of ODC. The data are consistent with an involvement of arachidonate cyclooxygenase products in the induction of rat hepatic ODC by the tumor promoters.