Induction of adaptive response in utero by ionizing radiation: A radiation quality dependent phenomenon

Investigation on possible induction of adaptive response (AR) by high-liner energy transfer (LET) particleradiation for protection against low-LET photon radiation-induced detrimental effects has not yet been performed inutero. This study verified if an AR could be induced by high-LET particle radiation from accelerated heavy ionsagainst low-LET X-ray radiation-induced detrimental effects on fetal mice. Total body irradiation of pregnantC57BL/6J mice were performed by delivering a priming dose ranging from 10 mGy to 320 mGy of particle radiationon gestation day 11 followed one day later by a challenge dose at 3500 mGy from X-ray radiation. The monoenergeticbeams of carbon, silicon and iron with the LET values of about 15, 55, and 200 KeV/μm, respectively, were examined.Significant suppression by the priming radiation of the detrimental effects (fetal death, malformation, or low bodyweight) was used as the endpoints for judgment of a successful AR induction on gestation day 18. Existence of ARwas not observed. On the other hand, the priming dose of high-LET particle radiation, in some cases, even increasedthe detrimental effects induced by the challenge dose from low-LET X-ray radiation. Although existence of ARinduced by high-LET radiation in cultured mammalian cells in vitro and in certain tissues of laboratory mice in vivowas demonstrated, the present study did not suggest that low dose of high-LET particle radiation could induce an ARin fetal mice inutero under the setup of our experimental system.