Effects of manganese compounds on carcinogenicity of nickel sub-sulfide in rats

Abstract

The effects of manganese compounds upon the carcinogenicity of αNi₃S₂ were tested in male Fischer rats. In Experiment I, rats were given i.m. injections of αNi₃S₂ (2.5 mg) and Mn dust (2.0 mg), singly or in combination. By 100 weeks, sarcomas occurred at the injection site in 0 of 24 rats in the vehicle control group, in 0 of 24 rats that received Mn dust alone, and in 23 of 24 rats that received αNi₃S₂ alone. Combined administration of αNi₃S₂ plus Mn dust as a single i.m. injection resulted in sarcomas in 14 of 23 rats (p versus αNi₃S₂ alone). In rats that received injections of αNi₃S₂ in one thigh and Mn dust in the opposite thigh, the sarcoma incidence at the site of αNi₃S₂ injection was 24 of 24 rats. In Experiment II, rats were given i.m. injections of αNi₃S₂ (1.2 mg) and Mn compounds (MnS, Mn₂O₃, MnO₂ or MN₂(CO)₁₀, in dosages equivalent to 1.0 mg of Mn), singly or in combination. No sarcomas occurred at the injection site in rats that received the vehicle or any of the manganese compounds alone. Sarcomas occurred in 13 of 27 rats that received αNi₃S₂ alone; this sarcoma incidence was not reduced by admixture of any of the Mn compounds. The median tumor latent period and the me- Wan survival period were significantly longer (p 3S₂, compared with rats that received αNi₃S₂ alone, suggesting that MnS may have weak anticarcinogenic effect. These experiments demonstrate that inhibition of αNi₃S₂-carcinogenesis by Mn dust is a local rather than a systemic effect, and that, with the possible exception of MnS, the other manganese compounds that were tested are ineffective as inhibitors of αNi₃S₂-carcinogenesis.