IN-VIVO BROMODEOXYURIDINE(BRDU)-LABELING INDEX OF RAT THYMUS - INFLUENCE OF DIFFERENT BRDU DOSES AND EXPOSURE TIMES AS ANALYZED BOTH IN TISSUE-SECTIONS AND IN SINGLE-CELL SUSPENSIONS

Tissue sections and single cell suspensions of rat thymus were analyze d by flow and image cytometry to study the effects of different doses of bromodeoxyuridine (BrdU) (10, 50 and 100 mg/kg and different labell ing periods (15, 30 and 60 min) on the BrdU-labelling index. The propo rtions of BrdU-labelled cells, as analyzed by flow cytometry, were sim ilar in the different groups of our study. However, the quality of the results was not exactly the same, since when the BrdU dose decreased, the separation between BrdU-positive S-phase cells and both the G(0)/ G(1) and the G(2)/M BrdU-negative cells on a DNA/BrdU histogram became less clear. On the other hand, the proportion of BrdU-labelled cells in tissue sections was greater in the groups of animals that received doses of 100 mg/kg and were killed 15, 30 or 60 min later than in the sections obtained from the remaining groups. Our results show that bot h hose and exposure time to BrdU may influence the final results when cell proliferation is assessed, the variations obtained clearly depend ing on the technique used for the immunological detection of BrdU-posi tive S-phase cells.