A quantitative method for evaluating the effects of drugs on bone marrow cellularity using the same experimental...

A method for quantifying the cellularity of rats bone marrow per unit of weight is described. Absolute numbers of each cell type per mg of bone marrow in the left and right femurs of the same experimental animal were determined at different times. In normal rats in which both femurs were studied simultaneously it was found that the absolute counts of each cell type per mg of bone marrow in the left and right femurs did not differ, nor were differences found in absolute numbers of marrow cells when the quantitative analyses from the left femurs were compared with those of the right femurs of the same animal, 10 and 20 days later. In order to test the validity of the present method for evaluating the effects of drugs on hematopoiesis, a single oral dose of busulphan (20 mg/kg), was administered to normal rats immediately after the marrow quantitative studies of the left femurs were performed. A marked and significant reduction in total nucleated cell was seen in marrows from the right femurs, 10 days later. Cellular effects were particularly pronounced on the myeloid line. Results presented here indicate that the quantitative study employed is a simple and useful method to evaluate the effects of drugs on hematopoiesis. The novelty of this method lies in: 1) its expression of cellularity on a per mg marrow basis, thereby avoiding possible misinterpretations of data which occur when results are expressed as percentages and 2) the analysis of contralateral femoral marrow specimens obtained from the same animal before and after drugs treatment. Therefore, each animal acts as its own control avoiding possible errors in the determination of drug-induced hematopoietic changes due to inter-animal variability.