[Analysis of chromosome aberrations and nucleolar organizer regions of chromosomes in workers producing pyromellitic dianhydride: the possibility of the adaptive role of Ag-NOR variants].

To assess the mutagenic danger of pyromellitic dianhydride (PMDA) production, the frequency of chromosome aberrations in peripheral blood lymphocytes from 56 workers and 37 control donors from Ufa was determined. A significant increase in the frequency of metaphases with aberrant chromosomes was found in the industrial group (5.3%) as compared with the control (2.9%). The effect of toxic factors on the functional state of acrocentric NORs was analyzed. No significant differences between PMDA-exposed workers and the control group in cumulative functional activity of 10 NORs (silver staining) was revealed. At the same time, a decreased proportion of cells with associations was found (76% in workers and 82% in donors), which may be a consequence of changes in immune status and in compensatory activation of cell proliferation, which leads to accumulation of young circulating lymphocytes with low associative capacity of acrocentrics. In addition, a significantly increased proportion of individuals carrying extreme Ag-NOR variants (grades 3.5-4.0) was observed in the industrial group (up to 37% vs 6% in the control), which may be due either to genotype selection at the number of active rRNA gene copies or to compensatory activation of repressed copies of ribosomal genes in some NORs.