Erythropoietic Cell Proliferation during Recovery from Acute Haemorrhage

SUMMARY Recovery of rats subjected to an acute haemorrhage by cardiac puncture has been followed during the subsequent 7 days. Cell proliferation in the spleen and bone marrow during this recovery process was studied by the autoradiographic technique. By 7 days, the circulating red cell volume was normal as judged by daily measurement of the haematocrit. Both the spleen and the bone marrow made approximately equal contributions to the recovery process. In addition, the liver made a very small contribution. It is suggested that the process of recovery is by stimulation of the stem cell compartment to produce more cells going through the erythroid maturation sequence. The maximum number of erythroid cells in the spleen occurs between 2 and 4 days and at this time the cells are dividing with a mean cycle time of about 15 hours. In returning to normal, this mean cycle time then gradually increases making less divisions during the maturation sequence possible and, therefore, producing mature cells at an increasingly slower rate. The marrow probably behaves in a similar manner but because it is a considerably larger and more diffuse organ than the spleen, the experimentally observed changes are not so dramatic and, therefore, less easily analysed.