Ornithine decarboxylase activity and the accumulation of its mRNA during early stages of liver regeneration.

The marked and well documented stimulation of hepatic ornithine decarboxylase (ODC; EC 4.1.1.17) in response to partial hepatectomy is at least to some extent attributable to an enhanced accumulation of the enzyme's mRNA. The stimulation of ODC activity was associated with an increased accumulation of two ODC-related mRNA species (2.1 and 2.6 kilobases; kb) as revealed by Northern blot hybridization analyses. The levels of the above-mentioned messages remained elevated for 6 h after partial hepatectomy, at which time the enzyme activity had returned to almost control levels. Furthermore, ODC protein levels remained relatively stable after the first peak of ODC activity, suggesting that posttranslational activity was responsible for the changes in ODC activity after the initial burst. In addition to the two mRNA species typical of mouse cells, rat tissues contained a third hybridizable message (1.6 kb). This smaller poly(A)+ RNA was never seen in samples obtained from mouse or human cells, but was always present in samples obtained from rat tissues. Interestingly this rat-specific message appeared to be expressed in somewhat opposite manner to the other two mRNA species.