| Abstract: | Regenerating mouse bone marrow cells were cultured i.p. in diffusion chambers (DC) to study factors affecting the maturation rate of granulocyte precursors. One day after exposing 3-day-old DC cultures to 3H-thymidine the cultures were harvested, and labelled proliferative and non-proliferative granulocytes were counted in radioautographs. The relative maturation rate--defined as the fraction of proliferative precursors maturing into the non-proliferative compartment per unit time--could be increased by different experimental procedures that inhibit cell production. Inhibition was obtained (a) by increasing culture cellularity; (b) by implanting DC into normal rats or rats with huge s.c. chloroma tumours rather than into mice; and (c) by treating the cells with leucocyte extracts (granulocyte chalone) during the last day of culture. Furthermore, a sudden inhibition of rapidly proliferating granulocytes by leucocyte extracts resulted in an increase (apparently transient) in the absolute number of labelled non-proliferative granulocytes. Such an increae was not detected in experiments involving a stronger or sustained inhibition of granulopoiesis, evidently because the size of the precursor population had been markedly reduced. |
