STUDIES ON ORNITHINE DECARBOXYLASE ACTIVITY IN NORMAL AND REGENERATING LIVERS

Ornithine decarboxylase activity was determined in the supernatant fraction of normal and regenerating livers. The enzyme was assayed by measuring 14CO2 release from [1-14C]ornithine or by isolation of labeled putrescine. Ornithine decarboxylase activity increases very shortly after partial hepatectomy and reaches a maximum at about 18 h following the operation. The rise in enzyme activity is synchronous with the changes in the incorporation of [14C]orotic acid into 28-S ribosomal RNA occurring during liver regeneration. Actinomycin D and puromycin inhibited the increase in ornithine decarboxylase activity found during regeneration. X-radiation is without effect on the increase in liver ornithine decarboxylase activity in partially hepatectomized animals. A single injection of thioacetamide or casein hydrolysate administration produce increases in liver ornithine decarboxylase activity of nonoperated rats. The hydrolysate effect is abolished by actinomycin. The results suggest that putrescine synthesis may be related to the changes in RNA metabolism occurring during liver regeneration. A mechanism is suggested that would account for the initial increase in ornithine decarboxylase activity following partial hepatectomy. © 1969.