Lack of ornithine decarboxylase activity in isolated rat liver parenchymal cells

Polyamines are associated with fundamental metabolic and functional steps in cell metabolism. The activity of ornithine decarboxylase, the key enzyme in polyamine metabolism, was followed during the preparation of rat liver parenchymal cells and in the isolated cells during incubation. In experiments in which ornithine decarboxylase was not induced in vivo, enzyme activity dropped to barely measurable values during the preparation. An even more drastic loss of enzyme activity was noted in livers in which ornithine decarboxylase activity was stimulated in vivo 20-40fold by previous injection of bovine growth hormone, or thioacetamide or elevated because of circadian rhythmical changes of the enzyme activity. Within the first 20 min of liver perfusion to disintegrate the tissue, ornithine decarboxylase activity decreased by up to 80%. The presence of bovine growth hormone during cell preparation cannot prevent the loss of enzyme activity. Incubation of the isolated cells for periods of up to 240 min did not restore the enzyme activity. Furthermore, incubation of the cells with bovine growth hormone did not induce ornithine decarboxylase, even though the medium was supplemented with amino acids in physiological concentrations. During normal liver perfusion and in contrast to the situation with isolated cells, there is no loss of enzyme activity but a small rise. Following pretreatment of the animals with bovine growth hormone or thioacetamide the highly stimulated activity of ornithine decarboxylase declined slowly during liver perfusion, but never dropped to values lower than normal for perfusion periods of up to 240 min. Moreover, in the intact perfused organ ornithine decarboxylase remains responsive to bovine growth hormone. The experiments demonstrate that enzymatic tissue dispersion by collagenase in particular or the preparation of isolated cells in general drastically alters the metabolic and functional state of rat liver parenchymal cells.