[The cytological mechanisms of the postnatal growth of aortic endothelium].

Contribution of proliferation and hypertrophy of endotheliocytes to the postnatal growth of the internal aortic lining in rats was estimated using organo- and cytometry, cytophotometry of nuclear DNA, radioautographic analysis of 3H-thymidine incorporation, determination of the mitotic index and the number of binucleated cells. Mitotic divisions of diploid endotheliocytes (in adult rats, their proportion attains 97-98%) is the principal cytological mechanism that, throughout the life of an animal, provides for an increase in the area of endothelial layer. Cell hypertrophy, which is unrelated to polyploidization, develops only during the first month of postnatal life. In old rats (2.5 years of age), an increased proportion of binucleate cells (2c x 2) and cells with pycnotic nuclei is observed.