Hepatocellular ultrastructure during liver regeneration after subtotal hepatectomy

Adult male rats were sacrificed at intervals between 24 and 120 hours after subtotal hepatectomy. Anesthetized and sham-operated control animals were included at each interval. At 24 and 30 hours after operation, the cytoplasm of the regenerating liver cells exhibited little rough or smooth endoplasmic reticulum and very few glycogen particles; however, the cytoplasm did contain numerous free ribosomes and abundant lipid bodies. By 36 hours, beginning reorganization of the rough endoplasmic reticulum was observed in the vicinity of hypertrophic Golgi complexes. This process continued at the 48- and 60-hour intervals, while the hepatocellular lipid progressively decreased. By the 72-hour interval, stratified layers of rough endoplasmic reticulum had reappeared in many parenchymal cells. At 96 and 120 hours after partial hepatectomy, most of the liver cells displayed essentially normal cytoplasmic components, including small glycogen deposits which were interspersed among elements of a slightly prominent smooth endoplasmic reticulum. Throughout the period of regeneration, hepatocellular nuclei were enlarged and irregular in outline. In many instances, the nucleoplasm exhibited prominent perichromatin and interchromatin granules; and, on occasion, the nuclei contained large chromatin clumps. Nucleoli were also enlarged, frequently were multiple, and often displayed a prominent small granule component. These morphologic features were observed in hepatic parenchymal cells during a period of active cellular proliferation. Many of these subcellular characteristics, however, have also been observed in neoplastic cells. It was proposed that these structural features were more likely associated with a rapid rate of cellular proliferation, than with any intrinsic properties of neoplasms.