Cellular mechanisms of the radiomodifying effect of hypothermia.

The irradiation of experimental tumors with a dose of 2000--2500 rad (20--25 J/kg) under hypothermia promoted an inhibition of the growth to a greater degree than the irradiation under normal conditions. In Guerin's tumor the inhibition of DNA and RNA synthesis was more expressed after the irradiation under hypothermic conditions than under the irradiation, and/or hypothermia alone. After the irradiation of the Guerin's tumor under hypothermia the cells were synchronized during the presynthetic phase of the cycle (block G1-S), and the effect of synchronization was more expressed in the tumor than in the normal tissue. The irradiation under hypothermia decreased the proliferative pool to a greater degree than the irradiation and/or hypothermia alone.