Detection of unscheduled DNA synthesis in hepatocytes isolated from rats treated with genotoxic agents: an in vivo- in vitro assay for potential carcinogens and mutagens.

An assay is described for the measurement of chemically-induced DNA repair in cultures of primary rat hepatocytes following in vivo treatment with genotoxic agents. Rats were exposed to chemicals then primary hepatocytes were isolated by liver perfusion and cultured with [3H]-thymidine. DNA repair was measured as unscheduled DNA synthesis (UDS) by quantitative autoradiography. Cells from control animals consistently ranged from -2 to -6 net grains (NG). Treatment of rats with 10, 1 or 0.1 mg/kg dimethylnitrosamine (DMN), i.p., yielded 36.6, 6.4 and -0.9 NG, respectively; 10 mg/kg DMN, per os (p.o.), produced 22.2 NG. Oral doses of 50 or 5 mg/kg acetylaminofluorene (AAF) yielded 14.0 and 6.4 NG, respectively. Carbon tetrachloride (CCl4) at 100 or 10 mg/kg, p.o., yielded -3.2 and -5.1 NG, respectively. Thus, dose-related increases in UDS were observed for the hepatocarcinogens DMN and AAF while vehicle controls and the hepatotoxin CCl4 produced no response. An examination of the time-course of DNA repair following DMN treatment shows a linear decline in UDS during the first 24 h post-treatment followed by a slower decline from 24 to 48 h. These results indicate that this assay is a potentially useful system for assessing the genotoxic and potential carcinogenic activity of chemicals in the whole animal.