Characterization and cell cycle kinetics of hepatocytes during rat liver regeneration: in vivo BrdUrd incorporation analysed by flow cytometry and electron microscopy.

The incorporation of bromodeoxyuridine (BrdUrd) into newly synthesized DNA has been analysed during hepatocellular regeneration induced by partial hepatectomy in young rats. The kinetic state of the liver has been studied by flow cytometric analysis of the incorporated BrdUrd, while the fine localization of DNA replication sites through the cell cycle has been investigated at the ultrastructural level by the immunogold technique. Eighteen hours after partial hepatectomy flow cytometry revealed an early S phase distribution which corresponded to a specific staining of the interchromatin domains of the hepatocyte nucleus. Thirty-four hours after hepatectomy, on the other hand, when most cells were in late S, a specific staining of heterochromatin domains was observed. The effect of the BrdUrd technique on nuclear aggregation has also been analysed and discussed. The results demonstrate that specific patterns of DNA replication can be recognized during the cell cycle and that flow cytometry and electron microscopy appear to be complementary in the kinetic study of liver regeneration.