Kinetics and cellularity of erythroblasts in the growing rat.

. Parameters of recognizable erythroid cell proliferation were measured in four groups of normal rats weighing 50, 100, 150 and 300 g in order to provide a comprehensive set of data suitable for a re-investigation of erythropoietic models. Total erythroblast cellularity was measured by the 59Fe technique, DNA synthesis time by quantitative 14C-autoradiography, and the erythrocyte production rate was derived from the increase with time of the erythrocyte labelling index after repeated injections of 3H-leucine. Furthermore, the relative erythroblast density was determined in the various morphological compartments. From the total erythroid cell mass in DNA synthesis and the absolute erythrocyte production rate, figures were derived for the mean DNA synthesis time of erythroid cells and compared with the directly measured ones. The discrepancies in all weight groups between direct and indirect determination of DNA synthesis time were considerable. In a previous study re-evaluation of comparable data in literature had revealed comparable inconsistencies. Since a critical discussion of possible errors in the experimental techniques does not indicate data acquisition to be the principal source of disagreement it is concluded that the type of model applied to describe how cells pass the boundaries of morphological cell compartments is of high significance. Models based on a sequential flux of cells through the individual compartments are inadequate for evaluation of the presented set of data.