No abstract

The cytotoxicity and mutagenicity of dimethylnitrosamine (DMN) was determined in the CHO/HGPRT system. Metabolic activation of the promutagen was achieved by use of liver homogenate supernatant (S9) prepared from Aroclor 1254-induced Sprague-Dawley rats. The cytotoxic and mutagenic effects of DMN were enhanced by the inclusion of calcium chloride in the incubation mix, and this enhancement was dependent on the presence of sodium phosphate. Under conditions that yielded maximal activity (10 mM calcium chloride, 10 mM magnesium chloride, 50 mM sodium phosphate), an apparent calcium phosphate precipitate was observed. DMN activity increased with increasing amounts of S9 protein over the range of 0.3-3.0 mg/ml in the S9 mix and appeared to plateau at higher concentrations. The mutagenicity of DMN can be described as 110 mutants/10(6) cells per mM DMN per mg/ml S9 protein per hour.

The induction of cytotoxicity, growth inhibition, specific locus mutations, and cytological alterations such as micronuclei, chromosome/chromatid aberrations, and sister chromatid exchanges by 5-bromodeoxyuridine (BudR) in Chinese hamster ovary cells was determined. BudR shows concentration-dependent increases in cytological alterations over the range of 5–500 µM, but it is mutagenic only at concentrations greater than 50 µM.