A total of 118 time-mated CF1 white mice were exposed when their fetuses were 9, 12 or 16 days to 7.4 W forward power of 2450 MHz microwave radiation for 4 min, a sub-lethal exposure. This resulted in mean absorptions of energy from 22.4 to 27.1 J/g, the degree of absorption being roughly in an inverse ratio to weight and gestation age. When these irradiated fetal mice were delivered normally and matured at 2 months of age, they were again exposed to the same radiation as previously but continuously until death as electronically monitored on a polygraph. A parallel group of 25 2-month-old controls were similarly irradiated, and the absorbed dose in J/g and the time in min to kill were taken as the measure of radiation tolerance or radiosensitivity of the originally irradiated fetuses.
Only those males initially exposed to microwave energies at 12 and 16 days gestation and females irradiated at 16 days gestation showed a slight but statistically significant reduction in the mean time to kill. Only the 12 day males showed a significant reduction in the mean absorbed dose at death. None showed mean absorbed doses greater than did the controls, hence there was no evidence of any acquired resistance to radiation effects. There were some side effects, however, in that all males initially exposed in utero had mean body weight significantly lower than did the control males at 2 months of age. Females initially irradiated at 16 days gestation were, at 2 months, statistically lighter in mean body weight than any of the other females, irradiated or controls. There was no significant difference between the sexes in J/g absorbed dose to kill at 2 months of age, but there was a significant lowering of the time to death for those males previously irradiated at 12 and 16 days gestation age; and females at 16 gestation days, compared with their respective controls.
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