[Ultrastructural transformation of guinea pig hepatocyte nuclei 2.5 hours after partial hepatectomy]

Ultrastructural changes of guinea-pig hepatocytes activated by partial hepatectomy were investigated in the period preceding the intensification of premitotic synthesis of protein and DNA, i. e. 2.5 hours after the operation, when the maximal increase of Acridine orange binding by DNP of these cells occurs. A disarrangement of the strand-like distribution patterns of condensed chromatin and margination of membrane-bound condensed chromatin was found. Morphometric analysis has shown some decrease of area occupied by condensed chromatin not bound with membrane and perinucleolar chromatin, and also a decrease in the number of isolated clumps of this chromatin. These finding may suggest some chromatin decondensation. At the same time, the condensed chromatin of most of hepatocytes reveals a righter packing of DNA fibrils. The nucleoli of activated hepatocytes increase in size and have a welll developed nucleolonemic structure and granular component; these pecularities corresponding to a high level of nucleolar RNA synthesis.