[Autoradiographic investigations on the effect of city smog extract on DNA synthesis and cell cycle of mammalian cells in vitro. I. Effect of city smog extract on DNA synthesis of kidney- and embryonic cells of the golden hamster in vitro (author's transl)].

We analysed the effect of city smog extract from Düsseldorf on DNA synthesis of mammalian cells in vitro. Airborne dust was extracted with aceton and thereafter transferred to dimethylsulfoxide. Dosage was calculated according to the benzo(a)pyrene content. We used logarithmically growing cultures of hamster kidney and embryonic cells. DNA synthesis was determined autoradiographically by incorporation of 3H-Thymidine. We found that city smog extract exerted a dose-dependent cytotoxic effect leading to a decrease of DNA synthesizing cells. High concentrations of city smog extract induced cell necrosis and suppressed DNA synthesis completely. Moderate doses of extract caused a dose-dependent, but temporary cessation of DNA synthesis. Cells resumed DNA synthesis after a certain delay. Low concentrations of city smog extract induced no detectable effects. Inhibition of DNA synthesis was evident already one hour after addition of extract. Therefore a direct effect on DNA metabolism could be supposed. Furthermore, exposed cultures demonstrated a delay in entrance of new cells into the DNA synthesis. Alterations in DNA synthesis could be of great importance for carcinogenesis, especially if we take in consideration the content of carcinogens in city smog extract.