DNA repair has been investigated, estimated by unscheduled DNA synthesis (UDS) and the cellular NAD+ pool, after exposing human mononuclear leukocytes to hyperthermia and γ radiation separately and in combination. It was found that γ radiation induced a decline in UDS with increasing temperature through the temperature region studied (37-45°C). At 42.5°C the γ-ray-induced UDS was reduced to about 70% of that at 37°C. Following γ-ray damage the NAD+ pool dropped to about 20% of control values. Without hyperthermic treatment the cells completely recovered to the original level within 5 hr. Moderate hyperthermia (42.5°C for 45 min) followed by γ-ray damage altered the kinetics so that even after 8 hr the NAD+ pool had recovered to only 70% of the original level. After heat treatment at 44°C for 45 min prior to γ radiation the cells did not recover at all, presumably because of the cytotoxic effects from the combined treatment.

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