Effect of gamma radiation on the foetal haemopoietic system in the mouse

Purpose: To study the effect of gamma irradiation, in the late foetal period, on the haemopoietic progenitor cells of the mouse foetus. Materials and Methods: Pregnant Swiss mice were exposed to 0.1 to 1.5 Gy of Cobalt-60 gamma radiation on the 17th day of gestation. At 24h (18 day p.c.) and 72h (20 day p.c.) after exposure the weights of foetal liver and spleen and their mean cellularity were determined. Chromosomal aberrations and micronuclei (MN) were studied at 94 h. Haemopoietic progenitor cell survival at 24 and 72h post-irradiation was studied by exogenous spleen colony assay. Results: Irradiation caused significant reduction in the weights of foetal liver and spleen, which was more pronounced at 72h postirradiation. The mean cellularity as well as the CFU-S₈ and CFU-S₁₂ of liver and spleen showed a radiation dose-dependent decrease, but the spleen showed a higher sensitivity than liver to doses below 1.0Gy. Chromosomal damage in liver increased linearly with dose, while in spleen the increase was linear-quadratic. Conclusions: Tim results demonstrate the damaging effect of low doses of gamma radiation on the late foetal haemopoietic progenitor cells of the mouse. Induction of cytogenetic damage appears to be a no-threshold effect in the dose range used.