Regulatory effects of corticosterone on ornithine decarboxylase activity during liver regeneration in rats.

Aims: The regulation of ornithine decarboxylase (ODC) gene expression and enzyme activity by corticosterone during rat liver regeneration induced by partial hepatectomy (PH) was evaluated. Methods: Bilateral adrenalectomies were performed on ether-anesthetized rats 3 days before PH. Corticosterone in sesame oil was injected subcutaneously to adrenalectomied rats. ODC mRNA, ODC protein and enzyme activity were detected by in situ hybridization, Western blot and high performance liquid chromatography (HPLC), respectively. Results: The ODC mRNA levels, protein accumulation and enzyme activity were lower in the intact liver compared to the regenerating liver. After PH, mRNA levels were remarkably enhanced in all groups and peaked at 5 h post-PH, and presented a persistent increase only in adrenalectomy rats during the regeneration process. Corticosterone treatment resulted in a dose-dependent decrease in ODC mRNA content after 5 h post-PH. ODC protein accumulation in adrenalectomy rats was higher than that in sham-adrenalectomy rats, but it decreased in corticosterone-treated (10 mg/kg) rats until 24 h post-PH, with a strong decline seen in 40 mg/kg corticosterone-treated rats. ODC activity was rapidly promoted, and the highest levels were observed at 6 h after PH in all groups. After corticosterone treatment, the activities declined significantly at 6 h post-PH, with the lowest value found in the 40 mg/kg group. Conclusions: Corticosterone treatment results in dose-dependent decreases in ODC mRNA and enzyme protein both in the intact liver and the regenerating liver. The change in ODC activity is partially related to alterations of ODC mRNA and protein accumulation.