Autoradiographic evidence for reutilization of DNA catabolites by granulocytopoiesis in the rat

The proliferating granulocyte precursor pool of rat bone marrow was labelled during DNA synthesis by continuous infusion and by single injection of 3H-thymidine (3H-TdR), as well as by single injection of 125I-iododeoxyuridine (125I-UdR). The appearance of neutrophilic granulocytes in the blood stream after these various labelling procedures was studied by autoradiography. Labelling patterns of blood neutrophils were identical during continuous infusion and after single injection of 3H-TdR, and 100% labelling of the blood compartment was achieved. This result indicated reutilization of DNA catabolites to occur in granulocytopoiesis leading to continuous availability of 3H-labelled DNA precursors even after a single injection of 3H-TdR. Attempts to suppress reutilization of label by infusion of cold thymidine 1 h after injection of 3H-TdR were unsuccessful. However, a change in the labelling pattern of blood neutrophils was seen after single injection of 125I-UdR, a DNA precursor poorly reutilized in comparison to 3H-TdR. This result provided further evidence for reutilization of DNA catabolites by the cell system investigated. A comprehensive discussion of the results indicates that thymidinemonophosphate is the biochemical level of reutilization in granulocytopoiesis.