Radiation biochemistry of the chicken embryo: DNA synthesis and DNA degradation following X-irradiation.

Chicken embryos were X-irradiated with a dose of 8 Gy. At a developmental stage of 15 days, desoxyribonucleic acid (DNA) synthesis, nucleoid sedimentation, viscosity of the alkaline cell lysates and DNA fragmentation were examined in brain and/or liver cells. Further studies aimed at the appearance of acid-soluble nucleic acid metabolites in the allantoic fluid. Complementary investigations comprised the in vitro activities of a DNase I and a DNase II of liver and brain cells as well as of the allantoic fluid of X-irradiated embryos. It could be shown for the first time that, following acute X-irradiation of the chicken embryo, the inhibition of DNA synthesis is accompanied by at least two enzymatic DNA degradation phases. The early phase comprises a period of 6 (-12) h, whereas the second phase lasts, with organ-specific peculiarities, > or = 24 h. During the early period, some apoptotic phenomena are seen, whereas at the later stages of radiation response signs of necrolysis become evident. The excretion of DNA metabolites, probably oligonucleotides, in the allantoic fluid is enhanced following X-irradiation > 2 Gy and may be used as an additional parameter of the overall radiation damage. Therefore, the chicken embryo may be regarded as a radiobiological and possibly toxicological alternative to laboratory animals with respect to the nucleic acid metabolism.