FORMATION OF CELL COLONIES IN X-IRRADIATED REGENERATING LIVERS OF RATS

Abstract

A high incidence of mitotic irregularities was observed when X-irradiated livers were induced to regenerate after a partial hepatectomy. Mitotic irregularities resulted in the formation of a heterogeneous cell population. As regeneration proceeded, the liver was found to be composed of two different cell populations: (i) one consisting of polyploid and aneuploid cells and incapable of giving rise to many descendants, and (ii) another consisting of apparently normal cells and capable of extensive proliferation which resulted in the formation of cell colonies. The regeneration of liver is mainly attributed to the cell colonies. No tumors appeared in the liver. These results demonstrate that a heterogeneous cell population of a "precancerous lesion" does not necessarily lead to the formation of a neoplasm. A selection pressure can be considered as necessary to favor the multiplication of cells with abnormal chromosome complements over that of cells with normal complements, as is seen in the livers of rats fed a chemical carcinogen. However, in the case of X-irradiated livers, normal cells seem to be favored.