Evaluation of the rat bone marrow and peripheral blood micronucleus test using monocrotaline

The present study was performed as part of the 9th collaborative trial of the CSGMT (Collaborative Study Group for the Micronucleus Test) to evaluate the performance of the rat micronucleus test in detection of clastogenic agents. Temporary fluorescent staining using acridine orange (AO) was compared with permanent staining using a modified Feulgen technique for bone marrow and Giemsa for blood. The Feulgen and AO methods were both found to be suitable for demonstrating micronucleus induction in rat bone marrow following oral administration of monocrotaline and cyclophosphamide. Induction of micronuclei was also shown using rat blood. The simple AO supravital method described produced uniformly stained preparations which were extremely easy to assess and interpret. The AO method was preferred to Giemsa for analysis of blood, but it was essential to analyse samples within 4 days of collection to avoid excessive deterioration of cells. Because of the relatively low number of micronucleated cells found in rat blood, it is suggested that examination of a larger number of cells may be necessary to achieve a similar sensitivity to the bone marrow assay for routine screening.