Granuloma pouch assay. II. Induction of 6-thioguanine resistance by MNNG and benzo[a]pyrene in vivo.

Growth of granulation tissue was initiated with croton oil on the inside of a subcutaneous air pouch, on the back of adult male rats. Two days later, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and benzo[a]pyrene (BP) were applied directly into the pouch in doses ranging from 0.05 to 1.8 mg and from 0.03 to 0.5 mg, resp. The granulation tissue was excised after 48 h. Isolated single cells were checked for their 6-thioguanine resistance in vitro. The influence of cell density during expression time in vitro, of 6-thioguanine concentration and cell density in selective media on the recovery of mutant cells was investigated. The spontaneous mutation frequency was 0.53 x 10(-5). There was a dose-dependent increase in mutation frequencies with both compounds. The frequency was 5 times as high with MNNG as with BP.