Studies on control of granulopoiesis in man. II. Influence of circulating neutrophil count on release of labelled bone marrow cells.

Leukocyte kinetic studies were performed by labelling neutrophilic leukocytes in vivo with radioactive diisopropylfluorophosphate and measuring the time taken for the label to traverse the myelocyte compartment, marrow granulocyte reservoir and blood (myelocyte-to-tissue transit time). Leukocyte specific activity (LSA) reached background levels within 17 to 22 days in normal subjects and more rapidly than normal in patients with neutropenia due to hypersplenism or marrow aplasia. When neutropenia was partially or completely corrected by splenectomy the label disappeared more slowly. In patients with stable neutrophilia the label disappeared slowly and a terminal plateau in the LSA curve was encountered. Analysis of LSA curves suggests that disappearance of labelled neutrophil cohorts is influenced by circulating neutrophil levels, not only by an effect on release of cells from the marrow granulocyte reservoir but also, directly or indirectly, by an effect on myelocyte proliferation.