RNA synthesis in rat liver cells with different DNA contents

The DNA content of mature rat liver parenchymal cells falls into three distinct classes with 1:2:4 amounts of DNA. These classes represent 2 N, 4 N, and 8 N cells. We have measured the changing proportions of these cells from 0.75 to 24 months of age. We have obtained a useful approximation for the numbers of each ploidy class, for cellular preparations from liver, as a function of the amount of DNA and age. Multiple linear regression analysis revealed that the average DNA content per cell is given by the relationship DNA/cell = 41.28(1/2)--324.14 Age1/4 + 499.37 Age1/8--207.24, with a multiple correlation coefficient of 0.990. Measurements of the amount of RNA synthesized in a 15-min period revealed that the relative proportions were 1.2:1.0 for 4 N:2 N cells of young rats, 1.3:1.1.:1.0 for 8 N:4 N:2 N cells of intermediate ages, and 1.1:1.0 for 8 N:4 N cells of old rats. The absolute amounts of RNA synthesized by each ploidy class declined with age.