Polyethylene glycol of molecular weight 400 (PEG-400) had a radioprotective effect of about 20% against lethality when given ip 20 min prior to single or fractionated X-ray doses to the head and neck. Dose modification factors (DMF) based on <tex-math>${\rm LD}_{50/15}$</tex-math> values ranged from 1.14 to 1.24. A similar DMF of 1.12 based on <tex-math>${\rm LD}_{50/30}$</tex-math> values was obtained using single doses of whole-body X irradiation. Mice given head and neck irradiation had significantly reduced rectal temperatures (31.3 ± 3.0°C) 9 days post irradiation compared with unirradiated controls (35.4 ± 0.6°C). No such reduction was observed when PEG-400 was given with radiation (36.3 ± 0.9°C). PEG-400 also lessened, but not significantly, the frequency of shivering in irradiated animals. Histopathologic examination of the oral structures demonstrated only marginal protection by PEG-400. Estimation of the α/β ratio from LD50 data on head and neck-irradiated mice yielded values of 4.4 ± 1.9 (95% confidence limits) Gy without PEG-400 and 7.9 ± 1.4 Gy with PEG-400. Since it is a nonthiol radioprotector, PEG-400 may be more useful when combined with more conventional thiol-containing radioprotectors.

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