Quantitative concentration-toxicity relationship for the injury of rat thymocytes by chemical compounds used in inter-laboratory toxicity ring-tests.

Rat thymic lymphocytes were used to determine the cytotoxic effect of the two toxicants, 3,4-dichloroaniline (DCA) and sodium bromide (NaBr), at concentrations that have effects in the 21-day reproduction test with Daphnia magna. To evaluate the effect of the chemical compounds on cell membrane integrity, we measured the permeability of the thymocytes to trypan blue and the leakage of lactate dehydrogenase (LDH) from the cells. The viability and metabolic activity of the thymocytes were quantified by the MTT assay. The DCA concentrations tested (from 31 to 310 nm) did not affect significantly the viability of thymocytes, as determined by trypan blue exclusion or by LDH leakage; however, with the MTT assay we could detect cytotoxicity at 62 nm. Both the trypan blue assay and the LDH assay indicated that concentrations of NaBr above 50 mm significantly affected the viability of the thymocytes. However, the MTT assay revealed a more pronounced toxic effect of NaBr, with significant cell damage being detected at 1 mm.