[Classes of nuclear size of human hepatocytes in aging]

The objective of these studies was to follow the development in human liver parenchyma of the size classes of nuclei and determine the variations with age in the volumes and numbers of individual classes. A total of 400 parenchymal liver cell nuclei were measured on each one of 8 micron thick sections of 10 livers obtained from subjects of all age groups. For this, we used the Pictoval type of micro-projection apparatus (VEB Carl Zeiss Jena) at a magnification of 3000 times. The largest and smallest diameters of nuclear sections were determined, and the volumes in micron3 were ascertained using a table published by Marzotko (1966). The decomposition of mixed distributions was by the graphic method of Daeves and Beckel (1958). The results obtained can be summarized as follows: 1. Whereas the nuclei in a seven-year-old boy contained the diploid or normal double complement of chromosomes, the proportion of this "regular class" was seen to drop to 70 percent in old age. 2. The proportion of the tetraploid size class was observed to increase to 20 percent. 3. Hypertetraploid nuclei were clearly seen to increase in proportion (to about 10 percent) even in old age. 4. Diploid nuclei increased in size up to the time of life between youth and old age. There was observed real nuclear growth. In old age, they are subject to shrinkage. 5. Tetraploid nuclei also seem to grow smaller in old age. 6. In the discussion an attempt is made to explain the process of formation of nuclear size classes and show the functional importance of polyploidization of parenchymal liver cell nuclei. The latter seems to be a quantitative increase of the genetic possibilities.