An unusual labeling index pattern of neutrophilic granulocytes after a 3H-thymidine flash labeling injection

After flash labeling of neutrophilic granulocyte precursors with 3H-Thymidine in 3 hematologically normal subjects the postinjection labeling indices (LI) and the labeling intensities of venous blood neutrophils were determined. The LI pattern during 18 days after injection showed a reproducible triphasic course of the LI curves: (a) a low "plateau", (b) a steep rise, (c) an undulating decrease until the end of the experiments. On the basis of these findings a simultaneous "at random" and "first in--first out" release of neutrophils from the postmitotic bone marrow compartment to the blood was suggested. Moreover, the intravascular half-life time of the neutrophils was determined as 9.3 h, the corresponding mean circulation time was 14 h. From the undulating course of the LI curves and the labeling intensity curves the duration of the mean neutrophil precursor cell cycle time in the mitotic bone marrow compartment was estimated to range between 19 and 24 h.