In vitro assay of the effect of antibacterial treatment of the intestinal flora on bone marrow cell proliferation. 1. Uptake by bone marrow cells of 3H-thymidine and some other radioactive precursors.

Some characteristics of the inhibition in bone marrow cell proliferation due to an artificial suppression of the intestinal flora have been investigated by means of an autoradiography. It appeared that the serum obtained from rats after oral treatment with neomycin sulphate (“neomycin-serum”) reduced the proportion of the 3H-thymidine labelled bone marrow cells in vitro by 13.3 ± 3.8 per cent (P < 0.0025) compared to control serum. This inhibition proved to be specific to the granulocytic cells of the bone marrow. In contrast, no effect in the amount or rate of DNA synthesis per cell was observed. It is suggested that the inhibitory effect of the “neomycin-serum” is mediated by the physiological control mechanisms (the chalone-antichalone system) of granulocytopoiesis. It is deduced, partly on theoretical grounds, that the inhibition in granulocytopoiesis observed in the present study results from a deficiency of antichalone (the mitotic stimulator of granulocytic progenitor cells) rather than from an excess of chalone (the mitotic inhibitor of granulocytic progenitor cells). The results are considered to support the view that in the homeostasis of granulocyte production, “tissue mass” (cell number) cannot be the sole reference value but that functional demand must also be significant.