The effect of actinomycin D on split-dose recovery and repopulation in jejunal crypt cells in vivo.

The effect of actinomycin D in combination with radiation on the survival of mouse jejunal crypt cells was measured using the microcolony technique. When administered 30 min before irradiation the drug was seen to enhance the cell killing of single doses of radiation. No significant changes in the rate or amount of repair in split-dose irradiation were found. Protracted split-dose intervals revealed cell repopulation commenced within 12 h after the first radiation dose. When given 6 h post-conditioning dose actinomycin D did not inhibit cell repopulation.