Inhibition of carcinogenic and clastogenic effects of N-nitrosomorpholine in rats immunized with tularemia vaccine.

The aim of the present work was to study whether immunization of rats with tularemia live vaccine (TLV) can influence carcinogenic and mutagenic action of N-nitrosomorpholine (NNM). The experiments were performed with male albino random-bred rats. The first group of rats was immunized with TLV 15 days before the start of experiment. These animals and the second group (positive control) were treated with NNM orally, (total dose was about 250 mg/rat). Rats including solvent (negative) control group were killed 12 months after the start of NNM treatment to study the carcinogenic effect. Experiments to study the influence of TLV on mutagenesis were performed with three groups of rats: the first (on 15th day after immunization with TLV) and the second group were injected intraperitoneally with NNM 100 mg/kg b.w. on 2 consecutive days, third group received only distilled water. The results of long-term experiment have shown that tumor incidence (both malignant and benign) in rats of positive control group was 74.2%. Immunized rats had significantly decreased incidence of tumors compared with the previous group--36.1%. Micronuclei level in bone marrow cells of non-immunized rats was statistically significantly higher than that in immunized rats. The inhibition of carcinogenic and clastogenic effects of NNM in rats immunized with TLV are probably due to a decrease in cytochrome P-450 activity. We suggest that immunization of rats with TLV can protect them against the cacinogenic and clastogenic actions of some chemicals.