EVALUATION OF LACI MUTATION IN GERM-CELLS AND MICRONUCLEI IN PERIPHERAL-BLOOD AFTER TREATMENT OF MALE LACI TRANSGENIC MICE WITH ETHYLNITROSOUREA, ISOPROPYLMETHANE SULFONATE OR METHYLMETHANE SULFONATE

Male C57Bl/6 lad transgenic mice were used to evaluate germ cell mutag enesis in vivo as part of a collaborative study. Groups of 10 mice wer e administered single intraperitoneal doses of ethylnitrosourea (ENU; 150 mg/kg), isopropyl methanesulfonate (IPMS; 200 mg/kg), methyl metha nesulfonate (MMS; 40 mg/kg) or vehicle, Epididymal spermatozoa and tes tes were recovered 3 days later and DNA isolated subsequently from epi didymal spermatozoa and seminiferous tubules were analyzed for lacI mu tations. The mutant frequency in seminiferous tubules (average+/-SEM) increased significantly compared with untreated controls (7.2+/-0.7x10 (-5)) following treatment with ENU (11.7+/-0.8x10(-5), p=0.003) or wit h IPMS (9.6+/-0.5x10(-5), p=0.018) but not following treatment with MM S (8.1+/-0.8x10(-5), p=0.213). Group mutant frequencies were not deter mined for epididymal spermatozoa from MMS- or IPMS-treated mice becaus e of poor DNA recoveries. As another indicator of the genotoxicity of these alkylating agents, the frequencies of micronuclei were determine d in the peripheral blood 48 h after carcinogen administration in the same transgenic mice. The micronuclei frequencies were elevated signif icantly(p<0.05) by each treatment(IPMS: 1.0%; MMS: 0.94%) compared to vehicle controls (0.3%). In a separate experiment, 40 mg/kg ENU was pr eviously found to increase the frequency of micronuclei in peripheral blood of lad transgenic mice 48 h after treatment (3.2%; Gibson et al. , 1995), These results demonstrate that the lacI transgenic mouse male germ cells are sensitive to some, but not all, mutagens under the con ditions used in this experiment. Investigation of other experimental d esigns would offer additional perspective on the usefulness of this tr ansgenic model for routine mutagenicity testing in germ cells.