Ethylene oxide (EtO), a potent monofunctional DNA alkylating agent, has been shown to induce sister chromatid exchanges (SCE) in the peripheral blood lymphocytes of animals and workers exposed to it in vivo. We have previously reported that elevations of SCE persist for 6 years after cessation of EtO exposure in cynomolgus monkeys chronically exposed to EtO; the elevation in mean SCE was entirely attributable to a subpopulation of high SCE frequency cells (HFCs). We now report that the detection of persistent HFCs is dependent on the conditions of cell growth, and that EtO exposure increases the replication indices of lymphocytes from the exposed animals when these cells are examined at early cytogenetic harvest times. Culture of lymphocytes in differing serum supplements, changes in cytogenetic harvest times, and alterations in in vitro incubation temperature all markedly affected mean SCE frequency by influencing the detection of HFCs. The frequency of EtO-induced HFCs was independent of 5-bromodeoxyuridine concentration, used for differential staining of sister chromatids. These observations indicate that the detection of persistent alkylation-induced chromosomal changes, observed long after cessation of in vivo chronic exposure of these animals, is highly dependent upon factors affecting cell growth.

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This work was supported by Center Grant ES-00002 from the NIH, by CCU902886 from the Center for Disease Control (K. T. K.), by a Faculty Development Award from the Mellon Foundation (K. T. K.), by CA43764 from the NCI (J. K. W.), and by the Office of Health and Environmental Research, US Dept. of Energy Contract DE-AC03-76-SF01012 (J. K. W.).

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