CORRELATION BETWEEN CIRCADIAN-RHYTHMS OF POLYAMINE SYNTHESIS AND CELL-PROLIFERATION IN RAT-LIVER

In rats fed ad lib, a marked circadian rhythm with a peak at night was observed in the hepatic level of ornithine decarboxylase (ODC) [EC 4.1.1.17], the enzyme for the 1st step of polyamine synthesis. A similar rhythm was found in the hepatic content of putrescine, but not spermidine or spermine. The mitotic activity of the liver exhibited a clear rhythm with a peak in the daytime. The rhythms of ODC and mitosis were generated by cyclic ingestion of proteinous food; the peaks shifted when rats were meal-fed and both activities disappeared on starvation or protein deprivation. The close parallel between the rhythms suggested that synthesis of polyamine, especially that of putrescine, was a prerequisite for the rhythmic growth of liver. The dietary induction of hepatic ODC depended on the nutritive value of dietary protein; zein or gelatin was effective only when supplemented with limiting amino acids. There was a good correlation between the hepatic ODC level and the relative growth rate.