Cytogenetic activity of methyl isocyanate in vivo in the mouse micronucleus test

The ability of methyl isocyanate (MIC) to induce mutagenic and cytotoxic effects in vivo in the mouse micronucleus test was evaluated by assessing the induction of micronuclei and depression of polychromatic erythrocytes in bone marrow and peripheral blood smears. Animals were exposed to MIC through intraperitoneal injection for 2 and 5 days in separate experiments, and bone marrow and peripheral blood were sampled 6 and 48 h after the last injection, respectively. MIC did not significantly increase the frequencies of micronucleated polychromatic erythrocytes (MN-PCE) and micronucleated normochromatic erythrocytes (MN-NCE) in bone marrow and peripheral blood samples respectively in either twice or multiply treated mice. However, a dose-dependent depression in percentage PCE observed was significant. This indicates that MIC exposure led to the cytotoxic effect by inhibition of bone marrow cell proliferation.