Radiation induced hemopoiesis in adult mouse liver.

Repeated whole-body irradiation of adult mice induced hemopoiesis in liver, as shown by the presence of stem cells (CFUS), progenitor cells of granulocytes and macrophages (CFUC) and foci of granulocytic cells. The largest numbers of CFUS (up to 700) were found 24 to 47 days after four doses of 450 rad x-rays given at 24 day intervals and 15-17 days after 2310 rad gamma radiation given at a low dose-rate (70 rad per day). CFUS were still present (although in smaller numbers) up to 210 days after four doses of 375 rad x-rays or 225 rad neutrons. CFUC were also present in liver after four doses of 450 rad x-rays, but their numbers could not be calculated accurately because of the marked inhibitory effect of liver cells on in vitro colony growth. Irradiation with one dose of 450 rad x-rays did not result in the appearance of CFUS in liver, suggesting that hepatic hemopoiesis can be induced by radiation only after repeated or prolonged bone marrow injury.