Incidence of micronuclei in cytokinesis-blocked lymphocytes of medical personnel occupationally exposed to ultrasound.

In order to investigate possible DNA damaging effects of ultrasound, the micronucleus assay on cytokinesis blocked human lymphocytes was performed. Preparations were stained by conventional Giemsa staining technique combined with additional staining techniques using fluorescent dye DAPI and silver nitrate. Blood samples were taken from medical personnel employed on ultrasonic scanning in medical diagnosis and unexposed control subjects from general population. Lymphocytes were cultivated in vitro at 37 degrees C. Cytochalasin-B in final concentration of 6 microg/ml was added 44 h after mitogen stimulation and cultures were harvested 28 h thereafter. Staining with both additional techniques can be used to distinguish micronuclei originating from breakage or mitotic loss of certain human chromosomes bearing DAPI-positively stained or silver-positively stained regions. The results obtained indicate statistically significant increases in total number of micronuclei and changes in their distribution in exposed subjects compared to control. Based on different intensity of DAPI staining signal-positive and signal-negative "type" of micronuclei are distinguished, while silver staining has revealed Ag-NOR+ and Ag-NOR- micronuclei. In exposed subjects a prevalence in number of Ag-NOR+ micronuclei over Ag-NOR-micronuclei compared to control was observed, indicating greater susceptibility of chromosomes from D and G groups to damage caused by continuous occupationally exposure to ultrasound. In spite of their limitations, our results indicate that combination of conventional Giemsa staining of micronuclei with fluorescent dye DAPI and silver nitrate staining techniques can be valuable complement to the standard micronucleus assay.