FRACTIONATED X-IRRADIATION OF THE MAMMALIAN EMBRYO AND CONGENITAL ANOMALIES
Pure strain CF/sub 1/ Swiss white mice were time-mated to provide 387 dated pregnancies resulting in 3,598 implantations. These were x-irradiated to 25 r twice during the embryonic period from 0.5 to 8.5 days after conception in order to test the effect of 50 r fractionated x irradiation on the early mammalian embryo. There were 36 combinations of the fractionated exposures within this period, in none of which were less than 54 implantations studied. The results following 50 r single exposure of the early embryo or 50 r fractionated into two equal exposures at least 24 hours and up to 7.5 days apart did not differ from each other with respect to resorptions, or total percentage which appeared to be normal. However, with fractionation there were fewer exencephalies, or brain hernias, and also fewer fetal deaths. While exencephaly did not occur frequently after 50 r x irradiation, it did occur in litters which had been irradiated to 25 r on any day from 0.5 to 8.5, regardless of when the other fraction of 25 r was delivered. Day 7.5 may be considered particularly vulnerable. Days 3.5 and 4.5 appeared to be the least vulnerable with any combination, a time just before implantation. It is concluded that the concept of a critical period, cannot be applied to the radiosensitivity of the nervous system since it has been demonstrated that the brain can be affected by exposure to roentgen rays at any time before its development has been completed, even before the initial cleavage of the fertilized egg. It is apparent, from this study, that the mouse embryo is radioresponsive in that congenital anomalies can be produced by roentgen rays from the time of conception at least until organogenesis is completed. Intrauterine deaths may develop following even very low level irradiations. The anomalies following early exposure are probably due to chromosomal aberrations and, following exposure during organogenesis, are probably due to disruptions in the morphogenetic movements of differentiation resulting from the killing of vulnerable cells. While tbe embryo has remarkable powers of topographic reorganization, it is still to be proved whether it can survive irradiation insult without some permanent damage. It is contended that x irradiation is an insult which results in a deficit embryo, fetus, newborn, and surviving adult when it is applied at any time prior to the completion of organogenesis. Extrapolation of radiation effects from the mouse embryo to the human is not valid. However, such findings suggest that not only should the embryo and fetus be protected against unnecessary x irradiation, but that fractionation of dose may reduce the incidence of some anomalies, but not tbe over-all damage to the embryo. 66 references. (C.H.)
- Research Organization:
- Columbia Univ., New York
- NSA Number:
- NSA-14-017715
- OSTI ID:
- 4161307
- Journal Information:
- Am. J. Roentgenol., Radium Therapy Nuclear Med., Vol. Vol: 84; Other Information: Orig. Receipt Date: 31-DEC-60
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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