A quantitative method for evaluating the effects of drugs on bone marrow cellularity using the same experimental animal. Quantification of the effects of a single dose of busulphan.

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.

A quantitative method for evaluating the effects of drugs on bone marrow cellularity using the same experimental animal. Quantification of the effects of a single dose of busulphan.

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.

Direct effects of thyroid hormones on bone marrow erythroid cells of rats.

A stimulatory effect on bone marrow cellularity was observed in normal and nephrectomized rats continuously infused with T3 and T4. Results of bone marrow studies are expressed in absolute numbers of total nucleated erythroid cells per milligram of femoral marrow at the beginning and after 8 hr of continuous intravenous infusions. Administration of T3 and T4 to nephrectomized rats produced a marked and significant increase in total erythroid cells counted. After differential analyses of the nucleated erythroid elements, a significant increase in all erythroid cell types was also observed. Similar results were seen in a control group of rats in which both ureters have been previously ligated and in groups of nephrectomized rats receiving rabbit antiserum against erythropoietin before starting the intravenous infusions of T3 and T4. These results indicate that stimulation of marrow erythropoiesis produced by thyroid hormones in our system is not dependent on renal or extra-renal production of erythropoietin. The progressive introduction of T3 and T4 into the circulation of rats with bilateral nephrectomy or ureter-ligated normal rats, may overload the mechanism of transport of these hormones in plasma. As a consequence, a progressive increase in free active forms of T3 and T4 in plasma may occur. Our interpretation of the present findings is that thyroid hormones stimulate directly bone marrow erythropoiesis. This stimulation is clearly evident when high levels of free active forms of thyroid hormones are present in plasma.