DNA synthesis in polyploid and binucleate hepatic cells in the regenerating rat liver of different ages.

In many vertebrate species, polyploid and binucleate cells are found in the adult hepatic parenchyma. The number of polyploid and binucleate hepatic cells increases with age. In this paper, the proliferative capacity of polyploid and binucleate cells were studied, in order to analyse a progressive reduction with age in the regenerative capacity of tissues. Three groups of rats, 4-week, 6-week and 15-week-old, were used in this experiment. The animals were partially hepatectomized, received an injection of tritiated-thymidine at 18 hours after the operation, and were sacrificed 30 minutes later. The livers were then subjected to the combined autoradiographic and microspectrophotometric studies. The labeling index was calculated for each hepatic cell type, which was classified according to nuclear polyploidy and binuclearity. Spatial distribution of polyploid cells in the liver lobule and that of hepatic cells labeled with tritiated-thymidine were also studied, and were taken into consideration to interpret values of the labeling index. The results of these studies indicate that value of the labeling index of polyploid hepatic cells is generally smaller than that of diploid cells, and that value of the labeling index of binucleate cells is also smaller than that of mononucleate cells. These results strongly suggest that the proliferative capacity of hepatic cells is reduced with polyploidization.