A single SC injection of 2-acetylaminofluorene (AAF) was given to pregnant C57BL/6 mice on day 15 of gestation, and the offspring subsequently given twice-weekly injections of phorbol for 25 weeks. Control groups included: (1) untreated; (2) AAF-treated mothers (kept under observation for 18 months, as with all the other groups); (3) untreated offspring of untreated mothers; (4) untreated offspring of AAF-treated mothers, and (5) phorbol-treated offspring of untreated mothers. The incidence of hepatomas in the phorbol-treated offspring of AAF-injected mothers was 8/74 (11%), as compared with 2/80 (2.5%) in the untreated offspring of AAF-injected mothers. The AAF-injected mothers themselves developed 3/36 (8%) hepatomas; while all othe other control groups were free from liver tumours. The development of reticulum cell sarcomas, and of a few cases of lung adenomas, in the various groups, was presumably spontaneous. The results seem sufficiently encouraging, as a model for the study of systemic carcinogenesis, to warrant further attempts at two-stage transplacental carcinogenesis, using other potential initiators and promoters.
A single subcutaneous injection of 200 mu Ci [3H] thymidine into pregnant BALD/c mice, followed by intraperitoneal injections of phorbol, twice weekly for 25 weeks, in the offspring, resulted in higher tumour development in the lungs and livers of male and, to a lesser extent, of female offspring, than in their untreated littermates. The difference in overall tumour incidence was statistically significant, but the increases of the individual tumour types were only of borderline significance. Slight carcinogenic activity of [3H]thymidine alone was observed in the mothers, and in the offspring, without phorbol treatment. The results suggest the possibility of using [3H]thymidine as a broad spectrum initiator for transplacental two-stage carcinogenicity studies to determine the organ specificity of different promoting agents.
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