Cell Proliferation Patterns in an Autogenous Rat Sarcoma23

Abstract

The cell proliferation pattern of the methylcholanthrene-induced autogenous rat sarcoma was investigated by continuous labeling with tritiated thymidine (³H-TDR), double-labeling with ³H-TDR and ¹⁴C-TDR, and by following the serial decay of the grain count frequency distribution after pulse labeling with ³H-TDR. The data showed that only 40–60% of the initial S cohort completed mitosis and entered the succeeding cycle. About 20–35% of the S cohort left the cycle for long residence in G2, and 20–40% of the residual S cohort, after mitosis, remained in G1 for long intervals. Cells subsequently re-entered the cycle from both nonproliferative compartments. The growth fraction was 39%, and the cells in G2_o and in G1_o were 38% and 23% of the population, respectively. The transit times of two-thirds of the G1_o cells were greater than 13 days, and for two-thirds of the cells in G2_o the transit times exceeded 1 week. The continual turnover of the proliferative and nonproliferative compartments was a major determinant of tumor growth.