Chromosomal responses to ionizing radiation reminiscent of and adaptive response in cultured Chinese hamster cells

When Chinese hamster V79 cells were internally exposed to low level chronic β-rays from incorporated tritiated thymidine (³H-dThd), the showed an “adaptive” response to the induction of chromosomal damage by subsequent higher acute doses of γ-rays.

The yield of sister-chromatid exchanges (SCEs) in the ³H-dThd pretreated cells was less than the yield induced by γ-rays alone (protective effects), and the micronucleus frequency was less than the sum of the induced frequencies by ³H-dThd and γ-rays separately (below-additivity effects). No adaptation to the micronucleus induction by γ-rays was observed after the ³H-adapted cells had divided once and when 3-aminobenzamide (3AB) was given before the challenge doses. The cross-resistance study revealed that the ³H-adapted cells were resistant to SCE induction but not to the micronucleus inductions by the challenge doses of reactor radiations. The results suggest that the SCE adaptation and the micronucleus adaptation or clastogenic adaptation are probably caused by different, inducible adaptive repair pathways.