BINUCLEATION AND POLYPLOIDIZATION PATTERNS IN DEVELOPMENTAL AND REGENERATIVE RAT-LIVER GROWTH

The hepatocellular binucleation rate, measured as the percentage of bi nuclear cells amongst newly formed bromodeoxyuridine-labelled and immu nostained collagenase-isolated rat hepatocytes, decreased from 12% to 4% between days 30 and 40 after birth, rose to 20% between days 50 and 60, and then declined again to the adult rate of about 10% at day 80. During regenerative growth following a two-thirds partial hepatectomy , the rate of binucleation declined to about 3%, causing the fraction of binuclear cells to fall from 27% (before hepactectomy) to 5% (at 45 h after hepactectomy) as pre-existing binuclear cells replicated and formed mononuclear daughter cells. Essentially all (97%) hepatocytes r eplicated at least once, starting their DNA synthesis at around 13 h a nd reaching a peak at 30 h, irrespective of ploidy and nuclearity. At later time points, the diploid hepatocytes had a higher labelling inde x than the polyploid cells, suggesting a greater tendency to go throug h several cell cycles.