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Nucleolar Behavior in Regenerating Liver of Normal and Whole-bodyirradiated Rats

Laboratory of Cellular Biology, Institute of Oncology, Bucharest, Romania

After partial removal of the liver in Wistar rats, the number of nucleoli in hepatocytes was found to be substantially reduced, especially in the periods preceding the outburst of mitoses. By delaying the appearance of mitotic waves by whole-body X-irradiation (1000 R) delivered prior to surgery, a more pronounced lowering of the nucleoli number was observed. Following each mitotic peak, developed within the first 50 hours after operation, the normal distribution of different nucleolar number categories was regained. With respect to the mechanism of this numerical reduction, some evidence is presented, indicating that either the whole or parts of nucleoli may be extruded in the extranuclear areas of regenerating liver cells.

Planar measurements demonstrated an important nucleolar volume enlargement, which took place particularly in the whole-body-irradiated animals. The specific cytochemical tests employed have shown that the intranucleolar structures containing RNA and/or lysine-rich proteins increased in both number and size, predominantly after X-irradiation followed by partial hepatectomy, exceeding by far the amounts observed in unirradiated liver cell nucleoli.

The internal structure of nucleoli, as revealed by toluidine blue-ammonium molybdate staining procedures, Methods A or B, was modified after whole-body irradiation, owing to the development of anisonucleolinosis.

Some possible mechanisms which could be involved in the numerical reduction and/or nucleolar enlargement phenomena, as well as those incriminated in the appearance of anisonucleolinosis, are suggested and discussed.

¹ Present address: Institute of Inframicrobiology, Sos. Mihai Bravu 285, Bucharest, Romania.

² Present address: Department of Histology, Faculty of Medicine, Bucharest, Romania.

Received 12/27/66. Accepted 5/29/67.