Ornithine decarboxylase activity and the accumulation of putrescine at early stages of liver regeneration

Abstract

intensive stimulation of ornithine decarboxylase (EC 4.1 .1.17, L-ornithine carboxylase) activity after partial hepatectomy of the rat belongs to the earliest biochemical changes in the regenerating liver remnant [l-4] . Enhanced ornithine decarboxylase activity results in a concomitant accumulation of liver putrescine [ 1,5,6] which in turn is supposed to stimulate the synthesis of spermidine [l] probably by activating the decarboxylation of S-adenosyl-L- methionine (Ado-met), the reaction needed for the synthesis of spermidine [7] . The activity of ornithine decarboxylase is almost maximally stimulated as early as at about 4 hr after partial hepatectomy and remains elevated for several days [2,6]. It has been reported that hypophysectomy, but not adrenalectomy, castration, or thyroidectomy, considerably delays, although does not prevent, the stimulation of ornithine decarboxylase after partial hepatectomy [8] . This latter observation might indicate the involvement of some humoral factor(s) in the regulation of putrescine synthesis in the regenerat- ing rat liver. In the present communication we have studied more closely the synthesis and accumulation of putrescine at early stages of liver regeneration. The results of several series of rats revealed that during the first day of regeneration the stimulation of ornithine decarboxylase appeared to occur in two phases, the first peak of the enzyme activity invariably occurring at 4 hr after the operation independently of the age of the animal. The stimulation of ornithine decarboxyl- ase was closely followed by an accumulation of putrescine. Evidence is also presented indicating that