Abstract
Previously, O6-methyl-guanine-DNA alkyltransferase (AT) of the chicken embryo has been investigated in vitro. In the present studies, the effect of in vivo (in ovo) treatment with methylnitrosourea (MNU) was examined at a developmental stage of 15 days and doses of 1.25-20 mg/egg, yielding about 1-16 mmol MNU/kg embryo weight. At intervals of 1-24 h, DNA of the brain was prepared. N7-methylguanine and O6-methylguanine were quantified by combining a rapid method of DNA isolation, high-pressure-liquid-chromatography (HPLC) and electrochemical detection of the guanine-alkyl adducts. In parallel, the AT activity of brain homogenates was determined. Within the range of the detection limits (N7-methylguanine: 16 nM, O6-methylguanine: 2.5 nM), no repair of the guanine adducts, being about 500 nmol O6-methyl- and 1800 nmol N7-methyl-adducts per mmol guanine 1 h following administration of 10 mg MNU/egg, was evident. The rather low acute toxicity of MNU in the chicken embryo at the 15th day of development DL50/24 h being > 4 mg MNU/embryo, argues, therefore, for an additional repair mechanism, e.g. cell replacement repair.
Published Version
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