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Factors influencing granulopoiesis have been evaluated using diffusion chambers implanted in the peritoneal cavity of rabbits. An increase in granulopoiesis in chambers implanted in hosts made neutropenic by nitrogen mustard occurs in mice made neutropenic by x-ray or drug. The intraperitoneal injection of leukocytes inhibited the growth of cells in chambers implanted in rabbits. Removal of mature granulocytes from marrow prior to chamber inoculation produced a marked in-increase in cell growth, especially of granulocytes. Mature granulocytes clearly inhibited cell replication and this inhibition involved both myeloid and erythroid elements, although the data suggest a greater effect on myelopoiesis. In contrast to the mouse, erythropoiesis in chambers in rabbits remained prominent for over 1 wk.

Studies were done of cell production by marrow in diffusion chambers implanted in the peritoneal cavity of rabbits subjected to various stimuli to hematopoiesis. In chambers in neutropenic hosts and in hosts injected with endotoxin, animals presumed to have an increased stimulus to granulopoiesis, there was increased production of granulocytes but there was also increased production of red cells. Although red cell production was decreased in chambers in polycythemic hosts, granulocyte production was not different from that in controls. Stimulation of erythropoiesis by erythropoietin injections or by exposure to hypoxia increased red cell production by marrow in the implanted diffusion chambers without diminishing granulopoiesis. Only in chambers in hosts made anemic by bleeding was there an increase in red cell production accompanied by a decrease in granulocyte production. In these anemic hosts induction of neutropenia led to an increase in granulopoiesis without any depression of erythropoiesis.