ANALYSIS OF CHROMOSOME-ABERRATIONS AND NU CLEOLAR ORGANIZER REGIONS (ORS) IN PYROMELLITIC DIANHYDRIDE-EXPOSED WORKERS - THE POSSIBLE ADAPTIVE ROLE OF AG-NOR VARIANTS

To assess the mutagenic danger of pyromellitic dianhydride (PMDA) prod uction, the frequency of chromosome aberrations in peripheral blood ly mphocytes from 56 workers and 37 control donors from Ufa was determine d. 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 sta te of acrocentric NORs was analyzed. No significant differences betwee n 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 wo rkers and 82% in donors), which may be a consequence of changes in imm une status and in compensatory activation of cell proliferation, which leads to accumulation of young circulating lymphocytes with low assoc iative capacity of acrocentrics. In addition, a significantly increase d 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.