Longterm effect of neonatal whole-body X-ray exposure on ploidy development in mouse liver cells

Mice of the strains C3H, DBA, NZB, and NMRI were X-irradiated with 0.475 Gy and 2.85 Gy (or 3.80 Gy) at newborn stage or at the age of six months. Their livers were prepared at the age of one to maximum 18 months and the hepatocytes isolated. The DNA content of both whole cells and separated nuclei was measured by flow cytometry and the liver ploidy pattern was determined applying a correcting calculation. Irradiation with 0.475 Gy of newborns of strain C3H results in a relative decrease of octoploid cells and an increase of tetraploid nuclei during lifetime (significance level of 0.001). After irradiation with 3.80 Gy a reversed reaction was observed. However, if the animals were irradiated as adults with a dose of 3.80 Gy the 8c cells decreased significantly three months later. Similarly, newborns of the outbred strain NMRI irradiated with 2.85 Gy, showed an increase of octoploid cells from the third month on, but an oscillating pattern of the 4c nuclear DNA content. In strains DBA and NZB, significantly altered ploidy values could not be found, perhaps due to a too great variance of experimental values.