Mercury chloride--and methyl mercury chloride--induced inhibition in NOR activity

Previous work has raised the question of whether mercury compounds inhibit the activity of the nucleolar organizing genes. For that reason we performed a cytophotodensitometric analysis on silver-stained interphase nuclei from human peripheral blood lymphocytes exposed to various concentrations of HgCl2 (0-150 X 10(-6) M), CH3HgCl (0-50 X 10(-6) M), and actinomycin D (0-0.1 microgram/ml). The last compound was used as a positive control. The cells were exposed to the compounds either during G1-early S phase, allowing recovery after the exposure, or from G1 until harvest; thus no recovery was allowed in this case. Like actinomycin D, both mercury compounds were shown to inhibit the NOR activity. This inhibition was furthermore more evident during the short exposure experiment. Our results do confirm that mercury compounds may, to a certain extent, influence some factors regulating the nucleolus-organizing activity.