We studied the possibility of using the micronucleus test in in vivo experiments on the model of rat follicular thyrocytes prestimulated to cell division (hemithyroidectomy). Single administration of N-nitroso-N-methylurea produced a significant dose-dependent effect on micronucleus formation in thyrocytes and polychromatophilic erythrocytes of the bone marrow. The test system allowed us to reveal a cumulative effect of 2-fold and 4-fold treatment with the mitogen in low or subthreshold doses on the thyroid gland. Our results indicate that the micronucleus test is an informative method for the analysis of the effect of genotoxic agents on the thyroid parenchyma.
Ploidy of thyroid parenchyma was studied in adult rats in the control and on day 9 after hemithyroidectomy; operated animals received 3 injections of N-nitroso-N-methylurea. The population of follicular thyrocytes is mainly diploid; total count of polyploid cells increased from 4.4% in the control to 8.5% in experimental rats. All thyrocytes containing micronuclei were tetraploid. No diploid micronucleated elements were detected. This suggests that genetically damaged thyrocytes divide by the mechanism of acytokinetic (polyploidizing) mitosis.
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