Nuclear growth and chromatin relaxation-condensation cycle in hepatocytes during the proliferative activation of rat liver.
In order to quantify the changes in nucleolar and nuclear volumes and in chromatin condensation produced during proliferative activation we have carried out morphometric studies on hepatocyte nuclei during rat liver regeneration using electron microscopy. To minimize the artefactual effects produced by fixation on subcellular structures we have fixed the livers by perfusion with glutaraldehyde. The mean values for the nucleolar and nuclear volumes were progressively increased until 28 h after 66% partial hepatectomy. The maximum values raised for the nuclei and nucleoli at this time were 3 and 4.28 times, respectively, those of controls. Later, nuclear and nucleolar volumes progressively declined. Two waves of diminution in nuclear electron-dense material were produced after hepatectomy. The first occurred between 0 and 12 h, with minimum values 1.34 times lower than those from control animals at 8 h. The second occurred between 12 and 28 h, with minimum values 2.56 times lower than those from control rats at 24 h. These two waves in chromatin relaxation correlate very well with the transcriptional changes described by other authors during the pre-replicative, replicative and mitotic phases of liver regeneration.