A quantitative study on the recovery of rat marrow erythropoietic cells after experimental suppression of erythropoiesis by repeated doses of cyclophosphamide.

Rat erythropoiesis was experimentally depressed by repeated doses of cyclophosphamide (CY) or by restriction of food consumption and the diagnostic value of quantitative haematology examinations of rat marrow erythroid morphology was evaluated. A slight depression of rat erythropoiesis (following a dose of 5 mg/kg/day) as well as a higher one (15 mg/kg/day) and the following recovery were determined by a quantitation of marrow erythroid morphology and by peripheral reticulocyte counts, yet a lower validity of peripheral erythrocyte and marrow relative erythroid cell counts was obtained; erythrocyte counts did not change even after a high depletion of marrow erythroid cells. The restriction of food consumption led to a similar depression of rat marrow erythropoiesis as that observed after CY administration. Our data may suggest that the quantitation of marrow erythroid morphology and peripheral reticulocyte counts are desirable in haematological examinations in preclinical safety evaluations performed on rats provided a new drug administered in repeated doses can be cytotoxic.