The effect of ionizing radiation, from a 100 Curie Cobalt-60 source, on diploid human cells grown in vitro has been investigated.
The analysed cell populations originated from foetal brain and lung tissue. Other known variations of this material were age and sex of the foetuses, primary and first transfer cultures.
The effect was measured by recording post-metaphase chromosomal aberrations in cell cultures fixed and stained 24 and 48 hours after acute irradiation. “Spontaneous” aberration frequencies were determined in matched control cultures.
Although conclusions must be guarded, in view of the insufficient knowledge of factors influencing human cell populations in vitro, our observations can be summarized, tentatively, in the following main points.
1. The frequency of “spontaneous” aberrations appears to vary with respect to (a) differences between the individuals from whom the biopsies were taken, (b) tissue of origin whether within or between individuals and (c) the sex of the cultured cells.
The qualified estimates of the overall averages of “spontaneous” aberrations were, (a) for the cell cultures derived from foetal lung 0.7 per cent (41/5,891 scored cells) and (b) for the cell cultures derived from foetal brain 2.5 per cent (21/851 scored cells).
2. In the irradiated cell cultures which received doses varying from 9-136 rads of absorbed dose the number of aberrant post-metaphases per 100 cells per rad varied from 0.10-0.15 for cultures derived from lung tissue and from 0.19-0.37 for cultures derived from brain tissue, all at 24 hours after the acute dose. At 48 hours after irradiation the frequencies were somewhat lower but the same trends remained.
3. The cell cultures derived from brain tissue appear to have a higher radio-sensitivity than those derived from lung tissue. Furthermore, a sexual dimorphism is suggested because, in all series of cultures, those composed of XY cells had a higher aberration frequency as compared to those with XX cells.
4. The irradiation doubling dose (for definition, see p. 27) was estimated at 15-40 rads (cf. table 7).