Hormonal control of erythropoiesis in canine cyclic haematopoiesis

The results of erythropoietin (ESF) studies in dogs with cyclic haematopoiesis are presented. Even though the dogs were exposed to a constant stimulus of hypoxia, cycles in the plasma ESF levels occurred at 11 to 12 day intervals. In some dogs, minor midcycle peaks were observed and the amount of ESF produced varied with the different animals. The peaks of ESF characteristically appeared approximately five days after onset of neutropenia. A hypothesis is presented to explain the known facts concerning canine cyclic haematopoiesis. It suggests that a poietin controlling factor is produced and that this assumed factor then stimulates the production of specific factors leading to increases of reticulocytes, platelets, and monocytes. The monocytes in turn produce more colony stimulating factor (CSF) leading to the formation of granulocytes. Such a sequence of events would explain the apogee of reticulocyte, platelet, and monocyte counts at a time when the nadir of granulocyte counts is reached.