Growth kinetics of Bp8 mouse ascites sarcoma after single dose whole body irradiation. I. Analysis of the relative and total numbers of cells in various parts of the cell cycle.

The effects of irradiation on the growth of the Bp8 mouse ascites sarcoma were analysed following doses of 1.75, 2.5, 5.0 and 8.0 Gy. From the total number of cells and the percentage of cells in G1, S-phase, G2 + M as measured by flow cytofluorometric DNA analysis and the mitotic index the total number of cells in the various parts of the cell cycle was estimated. After an initial delay in the increase in the cell numbers during the period of rapid growth the total number of cells shows a dose dependent decrease at the plateau stage of the ascites growth. This dose relationship is characterized by a shoulder type of curve with a D0 of about 6.5 Gy and Dq of about 2 Gy. This decrease in the total number of cells is caused by a decreasing number of G1, S-phase and mitotic cells while G2 cells generally remain at unchanged levels. This behaviour of the G2 cells reflects the preference of long-lasting blocking events in G2 of the cell cycle but may also indicate specific regulating processes linked to this type of cell. The ratio between the number of mitotic and G2 cells also decreases in a dose dependent way and is a sensitive indicator for irradiation effects even below the lowest dose (1.75 Gy) used in the present experiments.