Evidence for Several Mechanisms Involved in the Regulation of Ornithine Decarboxylase by Diamines During Rat Liver Regeneration.

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Abstract
The regulation of ornithine decarboxylase (ODC; EC 4.1.1.17) activity in regenerating rat liver by various amines appears to require at least 2 amino groups since only diamines or their derivatives inhibited the enzyme activity in vivo while all monoamines tested were largely ineffective. During very early periods of rat liver regeneration a single injection of 1,3-diaminopropane, a known potent inhibitor of ODC in vivo, produced a profund depression of ODC activity which was accompanied by a similar decrease in the apparent amount of enzyme protein as titrated with the aid of antiserum to rat liver ODC. In striking contrast to early regeneration, injection of diaminopropane during later periods of liver regeneration, while equally effectively depressing the enzyme activity, did not decrease the amount of immunoreactive enzyme protein, but markedly increased it. In support of the view that the mechanism of action of diamines is different during early and late phases of liver regeneration was the finding that putrescine and diaminopropane produced a longer lasting inhibition of ODC activity immediately after partial hepatectomy rather than 24 h later. The present results are in accordance with the idea that diamines have a direct action (transcriptional/translational?) on ODC during the supposed gene activation of the enzyme while an induction of macromolecular inhibitors or antizymes to ODC is a distinct feature of later periods of regeneration when the apparent gene activation has been completed.

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