[An assessment of the relative contribution of the processes of cellular proliferation, polyploidization and hypertrophy to the increase in liver mass at various stages in the postnatal development of rats].

Changes in isolated hepatocyte dry mass, its ploidy and liver mass at different stages of the rat postnatal ontogeny were investigated. The determination of these processes and special calculation made it possible to estimate quantitatively a relative contribution of cell proliferation, polyploidization and hypertrophy, not associated with DNA synthesis to the increase in the liver mass at different stages of the rat development. During the first week after the rat's birth, its liver growth is provided by 61 and 39% with hepatocyte proliferation and hypertrophy, respectively. Between the 14th and the 21st days of development, when considerable functional changes occur in the rat liver, the contributions of proliferative and polyploidization processes, and of cell hypertrophy into the liver mass increasing are roughly identical. Later on, the contribution of cell hypertrophy into the liver growth is noticeably reducing to reach within 1-2 months only 1%. On this developmental stage the liver mass increment by 2/3 is provided due to cell proliferation and by 1/3--to its polyploidization. As a whole, the accelerated growth of the rat liver from the birth to sex puberty is described as follows: the contribution of processes of proliferation and polyploidization, and of cell hypertrophy correspond to 28, 30 and 42%, respectively; afterwards, the liver growth being retarded. Within the period from 2 to 6 months, the liver mass increase is provided mainly (up to 76%) by cell proliferation, the shares of polyploidization and cell hypertrophy being 8 and 16%, respectively.