DNA Synthesis and Incorporation of P 32 in Irradiated Ehrlich Ascites Cells. ∗

Abstract

Summary

Experiments were carried out 4 to 6 days after inoculation of approximately 2 × 10⁷ Ehrlich ascites tumor cells in mice. When the 2-hour incorporation of P³² into DNA was measured at various times after irradiation (800 r total body x-irradiation), no significant depression in DNA specific activity was observed until 1 day. Measurements of mean cell volume, mean DNA content per cell, and mean total nucleic acid content per cell at 13 and 20 hours revealed that all 3 quantities increased at approximately the same rate, closely matching the growth rate of the unirradiated tumor and rate of DNA formation estimated from the incorporation data. The increased DNA content per nucleus after radiation was confirmed by Feulgen microspectrophotometry. At 48 hours after irradiation cell volume and total nucleic acid per cell had risen even higher while DNA per cell showed little further increase. The data suggest that the irradiated cells continue to synthesize DNA until they reach the premitotic DNA content (octoploid in Ehrlich cells) and are arrested there because they are unable to go through mitosis.